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 $66.98   12.272%   $75.1998   $75.20   $75.20   $75.20  
  Purchase #2 $204.82   10.213%   $225.7383   $225.74   $225.75   $225.70  
  Purchase #3 $110.82   13.445%   $125.7197   $125.72   $125.70   $125.70  
  Purchase #4 $47.34   6.744%   $50.5326   $50.53   $50.55   $50.50  
  Purchase #5 $58.61   3.138%   $60.4492   $60.45   $60.45   $60.40  
  Purchase #6 $226.31   3.387%   $233.9751   $233.98   $234.00   $234.00  
  Purchase #7 $64.48   3.630%   $66.8206   $66.82   $66.80   $66.80  
  7 purchase totals = $779.36       $838.4353   $838.44   $838.45   $838.30