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 $246.46   4.584%   $257.7577   $257.76   $257.75   $257.80  
  Purchase #2 $31.30   12.804%   $35.3077   $35.31   $35.30   $35.30  
  Purchase #3 $200.56   7.660%   $215.9229   $215.92   $215.90   $215.90  
  Purchase #4 $163.49   7.537%   $175.8122   $175.81   $175.80   $175.80  
  Purchase #5 $209.29   11.526%   $233.4128   $233.41   $233.40   $233.40  
  Purchase #6 $52.90   5.767%   $55.9507   $55.95   $55.95   $56.00  
  Purchase #7 $49.82   4.370%   $51.9971   $52.00   $52.00   $52.00  
  7 purchase totals = $953.82       $1,026.1611   $1,026.16   $1,026.10   $1,026.20