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 $44.65   9.163%   $48.7413   $48.74   $48.75   $48.70  
  Purchase #2 $107.94   8.258%   $116.8537   $116.85   $116.85   $116.90  
  Purchase #3 $247.89   3.130%   $255.649   $255.65   $255.65   $255.60  
  Purchase #4 $68.79   6.785%   $73.4574   $73.46   $73.45   $73.50  
  Purchase #5 $229.52   7.675%   $247.1357   $247.14   $247.15   $247.10  
  Purchase #6 $241.48   12.488%   $271.636   $271.64   $271.65   $271.60  
  Purchase #7 $199.69   12.368%   $224.3877   $224.39   $224.40   $224.40  
  7 purchase totals = $1,139.96       $1,237.8608   $1,237.87   $1,237.90   $1,237.80