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 $214.39   10.513%   $236.9288   $236.93   $236.95   $236.90  
  Purchase #2 $196.61   7.142%   $210.6519   $210.65   $210.65   $210.70  
  Purchase #3 $156.98   12.390%   $176.4298   $176.43   $176.45   $176.40  
  Purchase #4 $81.84   12.830%   $92.3401   $92.34   $92.35   $92.30  
  Purchase #5 $110.62   9.269%   $120.8734   $120.87   $120.85   $120.90  
  Purchase #6 $103.80   12.485%   $116.7594   $116.76   $116.75   $116.80  
  Purchase #7 $21.61   12.691%   $24.3525   $24.35   $24.35   $24.40  
  7 purchase totals = $885.85       $978.3359   $978.33   $978.35   $978.40