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 $38.96   12.599%   $43.8686   $43.87   $43.85   $43.90  
  Purchase #2 $198.51   3.585%   $205.6266   $205.63   $205.65   $205.60  
  Purchase #3 $205.49   5.675%   $217.1516   $217.15   $217.15   $217.20  
  Purchase #4 $12.95   12.872%   $14.6169   $14.62   $14.60   $14.60  
  Purchase #5 $57.35   10.396%   $63.3121   $63.31   $63.30   $63.30  
  Purchase #6 $169.93   13.550%   $192.9555   $192.96   $192.95   $193.00  
  Purchase #7 $200.63   9.281%   $219.2505   $219.25   $219.25   $219.30  
  7 purchase totals = $883.82       $956.7818   $956.79   $956.75   $956.90