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 $156.67   12.115%   $175.6506   $175.65   $175.65   $175.70  
  Purchase #2 $33.62   6.768%   $35.8954   $35.90   $35.90   $35.90  
  Purchase #3 $161.75   13.731%   $183.9599   $183.96   $183.95   $184.00  
  Purchase #4 $239.28   13.798%   $272.2959   $272.30   $272.30   $272.30  
  Purchase #5 $56.57   6.607%   $60.3076   $60.31   $60.30   $60.30  
  Purchase #6 $184.75   12.451%   $207.7532   $207.75   $207.75   $207.80  
  Purchase #7 $208.46   12.731%   $234.999   $235.00   $235.00   $235.00  
  7 purchase totals = $1,041.10       $1,170.8616   $1,170.87   $1,170.85   $1,171.00