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 $85.98   11.613%   $95.9649   $95.96   $95.95   $96.00  
  Purchase #2 $64.71   3.428%   $66.9283   $66.93   $66.95   $66.90  
  Purchase #3 $118.60   7.789%   $127.8378   $127.84   $127.85   $127.80  
  Purchase #4 $122.35   4.846%   $128.2791   $128.28   $128.30   $128.30  
  Purchase #5 $100.40   7.782%   $108.2131   $108.21   $108.20   $108.20  
  Purchase #6 $57.90   11.818%   $64.7426   $64.74   $64.75   $64.70  
  Purchase #7 $243.64   7.109%   $260.9604   $260.96   $260.95   $261.00  
  7 purchase totals = $793.58       $852.9262   $852.92   $852.95   $852.90