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 $233.94   8.604%   $254.0682   $254.07   $254.05   $254.10  
  Purchase #2 $47.61   13.867%   $54.2121   $54.21   $54.20   $54.20  
  Purchase #3 $59.92   11.484%   $66.8012   $66.80   $66.80   $66.80  
  Purchase #4 $84.65   7.655%   $91.13   $91.13   $91.15   $91.10  
  Purchase #5 $109.35   5.183%   $115.0176   $115.02   $115.00   $115.00  
  Purchase #6 $45.26   8.356%   $49.0419   $49.04   $49.05   $49.00  
  Purchase #7 $163.34   6.825%   $174.488   $174.49   $174.50   $174.50  
  7 purchase totals = $744.07       $804.7590   $804.76   $804.75   $804.70