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 $60.86   5.837%   $64.4124   $64.41   $64.40   $64.40  
  Purchase #2 $206.77   8.312%   $223.9567   $223.96   $223.95   $224.00  
  Purchase #3 $36.49   6.788%   $38.9669   $38.97   $38.95   $39.00  
  Purchase #4 $162.38   4.310%   $169.3786   $169.38   $169.40   $169.40  
  Purchase #5 $71.77   13.266%   $81.291   $81.29   $81.30   $81.30  
  Purchase #6 $23.40   13.252%   $26.501   $26.50   $26.50   $26.50  
  Purchase #7 $145.35   4.556%   $151.9721   $151.97   $151.95   $152.00  
  7 purchase totals = $707.02       $756.4787   $756.48   $756.45   $756.60