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 $85.30   12.466%   $95.9335   $95.93   $95.95   $95.90  
  Purchase #2 $27.36   8.683%   $29.7357   $29.74   $29.75   $29.70  
  Purchase #3 $243.31   4.229%   $253.5996   $253.60   $253.60   $253.60  
  Purchase #4 $89.71   12.148%   $100.608   $100.61   $100.60   $100.60  
  Purchase #5 $136.59   9.293%   $149.2833   $149.28   $149.30   $149.30  
  Purchase #6 $232.93   11.814%   $260.4484   $260.45   $260.45   $260.40  
  Purchase #7 $37.38   5.570%   $39.4621   $39.46   $39.45   $39.50  
  7 purchase totals = $852.58       $929.0706   $929.07   $929.10   $929.00