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 $184.31   8.333%   $199.6686   $199.67   $199.65   $199.70  
  Purchase #2 $218.97   10.636%   $242.2596   $242.26   $242.25   $242.30  
  Purchase #3 $126.78   10.830%   $140.5103   $140.51   $140.50   $140.50  
  Purchase #4 $125.82   13.493%   $142.7969   $142.80   $142.80   $142.80  
  Purchase #5 $75.63   12.663%   $85.207   $85.21   $85.20   $85.20  
  Purchase #6 $202.81   3.629%   $210.17   $210.17   $210.15   $210.20  
  Purchase #7 $160.81   13.634%   $182.7348   $182.73   $182.75   $182.70  
  7 purchase totals = $1,095.13       $1,203.3472   $1,203.35   $1,203.30   $1,203.40