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 $227.94   8.241%   $246.7245   $246.72   $246.70   $246.70  
  Purchase #2 $135.92   9.811%   $149.2551   $149.26   $149.25   $149.30  
  Purchase #3 $67.46   4.790%   $70.6913   $70.69   $70.70   $70.70  
  Purchase #4 $90.38   12.446%   $101.6287   $101.63   $101.65   $101.60  
  Purchase #5 $209.78   3.593%   $217.3174   $217.32   $217.30   $217.30  
  Purchase #6 $43.46   5.411%   $45.8116   $45.81   $45.80   $45.80  
  Purchase #7 $205.59   13.709%   $233.7743   $233.77   $233.75   $233.80  
  7 purchase totals = $980.53       $1,065.2029   $1,065.20   $1,065.15   $1,065.20