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 $121.85   4.151%   $126.908   $126.91   $126.90   $126.90  
  Purchase #2 $184.95   4.817%   $193.859   $193.86   $193.85   $193.90  
  Purchase #3 $58.61   9.199%   $64.0015   $64.00   $64.00   $64.00  
  Purchase #4 $183.29   13.763%   $208.5162   $208.52   $208.50   $208.50  
  Purchase #5 $175.35   6.521%   $186.7846   $186.78   $186.80   $186.80  
  Purchase #6 $143.80   4.628%   $150.4551   $150.46   $150.45   $150.50  
  Purchase #7 $62.34   5.570%   $65.8123   $65.81   $65.80   $65.80  
  7 purchase totals = $930.19       $996.3367   $996.34   $996.30   $996.40