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 $58.82   12.139%   $65.9602   $65.96   $65.95   $66.00  
  Purchase #2 $233.32   10.583%   $258.0123   $258.01   $258.00   $258.00  
  Purchase #3 $236.46   3.407%   $244.5162   $244.52   $244.50   $244.50  
  Purchase #4 $236.69   11.837%   $264.707   $264.71   $264.70   $264.70  
  Purchase #5 $89.42   7.131%   $95.7965   $95.80   $95.80   $95.80  
  Purchase #6 $179.71   13.297%   $203.606   $203.61   $203.60   $203.60  
  Purchase #7 $43.42   6.480%   $46.2336   $46.23   $46.25   $46.20  
  7 purchase totals = $1,077.84       $1,178.8318   $1,178.84   $1,178.80   $1,178.80