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 $238.89   11.671%   $266.7709   $266.77   $266.75   $266.80  
  Purchase #2 $195.91   4.716%   $205.1491   $205.15   $205.15   $205.10  
  Purchase #3 $207.76   6.749%   $221.7817   $221.78   $221.80   $221.80  
  Purchase #4 $123.45   12.237%   $138.5566   $138.56   $138.55   $138.60  
  Purchase #5 $75.34   12.644%   $84.866   $84.87   $84.85   $84.90  
  Purchase #6 $247.59   3.484%   $256.216   $256.22   $256.20   $256.20  
  Purchase #7 $138.94   10.172%   $153.073   $153.07   $153.05   $153.10  
  7 purchase totals = $1,227.88       $1,326.4133   $1,326.42   $1,326.35   $1,326.50