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 $62.94   9.836%   $69.1308   $69.13   $69.15   $69.10  
  Purchase #2 $197.76   4.339%   $206.3408   $206.34   $206.35   $206.30  
  Purchase #3 $13.53   10.337%   $14.9286   $14.93   $14.95   $14.90  
  Purchase #4 $157.71   11.563%   $175.946   $175.95   $175.95   $175.90  
  Purchase #5 $12.42   12.453%   $13.9667   $13.97   $13.95   $14.00  
  Purchase #6 $194.95   7.381%   $209.3393   $209.34   $209.35   $209.30  
  Purchase #7 $153.89   6.182%   $163.4035   $163.40   $163.40   $163.40  
  7 purchase totals = $793.20       $853.0557   $853.06   $853.10   $852.90