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 $53.27   11.872%   $59.5942   $59.59   $59.60   $59.60  
  Purchase #2 $104.33   8.793%   $113.5037   $113.50   $113.50   $113.50  
  Purchase #3 $23.57   11.245%   $26.2204   $26.22   $26.20   $26.20  
  Purchase #4 $105.71   13.255%   $119.7219   $119.72   $119.70   $119.70  
  Purchase #5 $224.51   11.749%   $250.8877   $250.89   $250.90   $250.90  
  Purchase #6 $71.41   5.362%   $75.239   $75.24   $75.25   $75.20  
  Purchase #7 $107.78   12.751%   $121.523   $121.52   $121.50   $121.50  
  7 purchase totals = $690.58       $766.6899   $766.68   $766.65   $766.60