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 $93.71   10.263%   $103.3275   $103.33   $103.35   $103.30  
  Purchase #2 $195.87   13.264%   $221.8502   $221.85   $221.85   $221.90  
  Purchase #3 $177.91   12.193%   $199.6026   $199.60   $199.60   $199.60  
  Purchase #4 $205.78   7.702%   $221.6292   $221.63   $221.65   $221.60  
  Purchase #5 $5.29   7.597%   $5.6919   $5.69   $5.70   $5.70  
  Purchase #6 $236.86   12.480%   $266.4201   $266.42   $266.40   $266.40  
  Purchase #7 $27.36   10.750%   $30.3012   $30.30   $30.30   $30.30  
  7 purchase totals = $942.78       $1,048.8227   $1,048.82   $1,048.85   $1,048.80