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 $71.49   4.479%   $74.692   $74.69   $74.70   $74.70  
  Purchase #2 $145.76   11.503%   $162.5268   $162.53   $162.55   $162.50  
  Purchase #3 $83.47   10.303%   $92.0699   $92.07   $92.05   $92.10  
  Purchase #4 $149.94   9.721%   $164.5157   $164.52   $164.50   $164.50  
  Purchase #5 $205.86   13.862%   $234.3963   $234.40   $234.40   $234.40  
  Purchase #6 $57.43   4.475%   $60   $60.00   $60.00   $60.00  
  Purchase #7 $61.33   8.141%   $66.3229   $66.32   $66.30   $66.30  
  7 purchase totals = $775.28       $854.5236   $854.53   $854.50   $854.50