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 $229.73   12.413%   $258.2464   $258.25   $258.25   $258.20  
  Purchase #2 $136.42   4.616%   $142.7171   $142.72   $142.70   $142.70  
  Purchase #3 $60.25   10.439%   $66.5395   $66.54   $66.55   $66.50  
  Purchase #4 $130.46   7.817%   $140.6581   $140.66   $140.65   $140.70  
  Purchase #5 $214.46   12.646%   $241.5806   $241.58   $241.60   $241.60  
  Purchase #6 $169.79   7.498%   $182.5209   $182.52   $182.50   $182.50  
  Purchase #7 $249.60   8.557%   $270.9583   $270.96   $270.95   $271.00  
  7 purchase totals = $1,190.71       $1,303.2209   $1,303.23   $1,303.20   $1,303.20