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 $65.46   8.780%   $71.2074   $71.21   $71.20   $71.20  
  Purchase #2 $33.78   12.751%   $38.0873   $38.09   $38.10   $38.10  
  Purchase #3 $39.54   11.139%   $43.9444   $43.94   $43.95   $43.90  
  Purchase #4 $200.46   10.387%   $221.2818   $221.28   $221.30   $221.30  
  Purchase #5 $126.90   6.873%   $135.6218   $135.62   $135.60   $135.60  
  Purchase #6 $17.97   5.396%   $18.9397   $18.94   $18.95   $18.90  
  Purchase #7 $203.34   8.781%   $221.1953   $221.20   $221.20   $221.20  
  7 purchase totals = $687.45       $750.2777   $750.28   $750.30   $750.20