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 $189.95   10.311%   $209.5357   $209.54   $209.55   $209.50  
  Purchase #2 $11.26   13.191%   $12.7453   $12.75   $12.75   $12.70  
  Purchase #3 $150.99   3.527%   $156.3154   $156.32   $156.30   $156.30  
  Purchase #4 $241.95   5.697%   $255.7339   $255.73   $255.75   $255.70  
  Purchase #5 $217.32   13.617%   $246.9125   $246.91   $246.90   $246.90  
  Purchase #6 $105.46   13.189%   $119.3691   $119.37   $119.35   $119.40  
  Purchase #7 $212.82   4.806%   $223.0481   $223.05   $223.05   $223.00  
  7 purchase totals = $1,129.75       $1,223.6600   $1,223.67   $1,223.65   $1,223.50