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 $207.53   9.766%   $227.7974   $227.80   $227.80   $227.80  
  Purchase #2 $113.83   9.834%   $125.024   $125.02   $125.00   $125.00  
  Purchase #3 $89.89   11.818%   $100.5132   $100.51   $100.50   $100.50  
  Purchase #4 $44.60   10.749%   $49.3941   $49.39   $49.40   $49.40  
  Purchase #5 $168.49   5.227%   $177.297   $177.30   $177.30   $177.30  
  Purchase #6 $96.89   6.445%   $103.1346   $103.13   $103.15   $103.10  
  Purchase #7 $8.64   13.692%   $9.823   $9.82   $9.80   $9.80  
  7 purchase totals = $729.87       $792.9833   $792.97   $792.95   $792.90