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 $205.61   8.762%   $223.6255   $223.63   $223.65   $223.60  
  Purchase #2 $8.85   3.685%   $9.1761   $9.18   $9.20   $9.20  
  Purchase #3 $169.65   7.829%   $182.9319   $182.93   $182.95   $182.90  
  Purchase #4 $62.30   8.550%   $67.6267   $67.63   $67.65   $67.60  
  Purchase #5 $92.98   6.184%   $98.7299   $98.73   $98.75   $98.70  
  Purchase #6 $9.72   3.557%   $10.0657   $10.07   $10.05   $10.10  
  Purchase #7 $7.59   3.552%   $7.8596   $7.86   $7.85   $7.90  
  7 purchase totals = $556.70       $600.0154   $600.03   $600.10   $600.00