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 $201.97   12.529%   $227.2748   $227.27   $227.25   $227.30  
  Purchase #2 $40.76   13.377%   $46.2125   $46.21   $46.20   $46.20  
  Purchase #3 $55.70   4.394%   $58.1475   $58.15   $58.15   $58.10  
  Purchase #4 $152.92   12.168%   $171.5273   $171.53   $171.55   $171.50  
  Purchase #5 $238.53   13.743%   $271.3112   $271.31   $271.30   $271.30  
  Purchase #6 $225.37   6.781%   $240.6523   $240.65   $240.65   $240.70  
  Purchase #7 $167.74   8.523%   $182.0365   $182.04   $182.05   $182.00  
  7 purchase totals = $1,082.99       $1,197.1621   $1,197.16   $1,197.15   $1,197.10