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 $226.44   8.192%   $244.99   $244.99   $245.00   $245.00  
  Purchase #2 $12.97   9.438%   $14.1941   $14.19   $14.20   $14.20  
  Purchase #3 $58.81   12.249%   $66.0136   $66.01   $66.00   $66.00  
  Purchase #4 $196.32   7.443%   $210.9321   $210.93   $210.95   $210.90  
  Purchase #5 $118.73   10.639%   $131.3617   $131.36   $131.35   $131.40  
  Purchase #6 $29.58   13.156%   $33.4715   $33.47   $33.45   $33.50  
  Purchase #7 $53.34   4.721%   $55.8582   $55.86   $55.85   $55.90  
  7 purchase totals = $696.19       $756.8212   $756.81   $756.80   $756.90