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 $217.91   10.729%   $241.2896   $241.29   $241.30   $241.30  
  Purchase #2 $8.33   3.262%   $8.6017   $8.60   $8.60   $8.60  
  Purchase #3 $223.85   10.674%   $247.7437   $247.74   $247.75   $247.70  
  Purchase #4 $94.93   11.872%   $106.2001   $106.20   $106.20   $106.20  
  Purchase #5 $94.80   4.752%   $99.3049   $99.30   $99.30   $99.30  
  Purchase #6 $55.38   7.783%   $59.6902   $59.69   $59.70   $59.70  
  Purchase #7 $199.91   4.231%   $208.3682   $208.37   $208.35   $208.40  
  7 purchase totals = $895.11       $971.1984   $971.19   $971.20   $971.20