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 $61.33   3.631%   $63.5569   $63.56   $63.55   $63.60  
  Purchase #2 $209.71   9.365%   $229.3493   $229.35   $229.35   $229.30  
  Purchase #3 $133.28   11.434%   $148.5192   $148.52   $148.50   $148.50  
  Purchase #4 $102.93   5.522%   $108.6138   $108.61   $108.60   $108.60  
  Purchase #5 $126.36   6.594%   $134.6922   $134.69   $134.70   $134.70  
  Purchase #6 $41.77   5.818%   $44.2002   $44.20   $44.20   $44.20  
  Purchase #7 $94.86   11.703%   $105.9615   $105.96   $105.95   $106.00  
  7 purchase totals = $770.24       $834.8931   $834.89   $834.85   $834.90