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 $90.58   6.618%   $96.5746   $96.57   $96.55   $96.60  
  Purchase #2 $79.96   8.750%   $86.9565   $86.96   $86.95   $87.00  
  Purchase #3 $170.29   3.506%   $176.2604   $176.26   $176.25   $176.30  
  Purchase #4 $178.74   13.830%   $203.4597   $203.46   $203.45   $203.50  
  Purchase #5 $186.54   11.436%   $207.8727   $207.87   $207.85   $207.90  
  Purchase #6 $7.67   4.276%   $7.998   $8.00   $8.00   $8.00  
  Purchase #7 $60.44   11.645%   $67.4782   $67.48   $67.50   $67.50  
  7 purchase totals = $774.22       $846.6001   $846.60   $846.55   $846.80