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 $189.91   9.837%   $208.5914   $208.59   $208.60   $208.60  
  Purchase #2 $60.88   8.862%   $66.2752   $66.28   $66.30   $66.30  
  Purchase #3 $81.76   9.449%   $89.4855   $89.49   $89.50   $89.50  
  Purchase #4 $92.37   5.741%   $97.673   $97.67   $97.65   $97.70  
  Purchase #5 $126.80   5.690%   $134.0149   $134.01   $134.00   $134.00  
  Purchase #6 $96.73   7.476%   $103.9615   $103.96   $103.95   $104.00  
  Purchase #7 $53.29   3.857%   $55.3454   $55.35   $55.35   $55.30  
  7 purchase totals = $701.74       $755.3469   $755.35   $755.35   $755.40