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 $32.97   7.850%   $35.5581   $35.56   $35.55   $35.60  
  Purchase #2 $173.87   7.553%   $187.0024   $187.00   $187.00   $187.00  
  Purchase #3 $126.55   5.552%   $133.5761   $133.58   $133.60   $133.60  
  Purchase #4 $146.32   6.283%   $155.5133   $155.51   $155.50   $155.50  
  Purchase #5 $186.57   7.712%   $200.9583   $200.96   $200.95   $201.00  
  Purchase #6 $204.26   8.659%   $221.9469   $221.95   $221.95   $221.90  
  Purchase #7 $121.86   3.680%   $126.3444   $126.34   $126.35   $126.30  
  7 purchase totals = $992.40       $1,060.8995   $1,060.90   $1,060.90   $1,060.90