Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.48   8.358%   $206.4003   $206.40   $206.40   $206.40  
  Purchase #2 $141.41   12.614%   $159.2475   $159.25   $159.25   $159.20  
  Purchase #3 $232.33   5.603%   $245.3474   $245.35   $245.35   $245.30  
  Purchase #4 $187.57   7.505%   $201.6471   $201.65   $201.65   $201.60  
  Purchase #5 $156.96   11.495%   $175.0026   $175.00   $175.00   $175.00  
  Purchase #6 $131.28   11.126%   $145.8862   $145.89   $145.90   $145.90  
  Purchase #7 $117.72   6.433%   $125.2929   $125.29   $125.30   $125.30  
  7 purchase totals = $1,157.75       $1,258.8240   $1,258.83   $1,258.85   $1,258.70