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 $95.27   3.121%   $98.2434   $98.24   $98.25   $98.20  
  Purchase #2 $81.64   13.116%   $92.3479   $92.35   $92.35   $92.30  
  Purchase #3 $174.94   13.115%   $197.8834   $197.88   $197.90   $197.90  
  Purchase #4 $205.80   6.302%   $218.7695   $218.77   $218.75   $218.80  
  Purchase #5 $108.56   7.555%   $116.7617   $116.76   $116.75   $116.80  
  Purchase #6 $116.73   8.676%   $126.8575   $126.86   $126.85   $126.90  
  Purchase #7 $206.55   12.541%   $232.4534   $232.45   $232.45   $232.50  
  7 purchase totals = $989.49       $1,083.3168   $1,083.31   $1,083.30   $1,083.40