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 $118.91   6.211%   $126.2955   $126.30   $126.30   $126.30  
  Purchase #2 $62.35   5.357%   $65.6901   $65.69   $65.70   $65.70  
  Purchase #3 $228.41   12.642%   $257.2856   $257.29   $257.30   $257.30  
  Purchase #4 $211.64   5.313%   $222.8844   $222.88   $222.90   $222.90  
  Purchase #5 $97.86   12.582%   $110.1727   $110.17   $110.15   $110.20  
  Purchase #6 $82.57   3.578%   $85.5244   $85.52   $85.50   $85.50  
  Purchase #7 $114.46   9.274%   $125.075   $125.08   $125.10   $125.10  
  7 purchase totals = $916.20       $992.9277   $992.93   $992.95   $993.00