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 $58.91   7.539%   $63.3512   $63.35   $63.35   $63.40  
  Purchase #2 $194.50   11.544%   $216.9531   $216.95   $216.95   $217.00  
  Purchase #3 $176.70   4.293%   $184.2857   $184.29   $184.30   $184.30  
  Purchase #4 $180.75   13.598%   $205.3284   $205.33   $205.35   $205.30  
  Purchase #5 $88.96   12.751%   $100.3033   $100.30   $100.30   $100.30  
  Purchase #6 $16.63   6.743%   $17.7514   $17.75   $17.75   $17.80  
  Purchase #7 $146.86   7.305%   $157.5881   $157.59   $157.60   $157.60  
  7 purchase totals = $863.31       $945.5612   $945.56   $945.60   $945.70