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 $54.66   11.306%   $60.8399   $60.84   $60.85   $60.80  
  Purchase #2 $231.38   6.674%   $246.8223   $246.82   $246.80   $246.80  
  Purchase #3 $167.29   13.442%   $189.7771   $189.78   $189.80   $189.80  
  Purchase #4 $109.72   6.379%   $116.719   $116.72   $116.70   $116.70  
  Purchase #5 $61.57   6.347%   $65.4778   $65.48   $65.50   $65.50  
  Purchase #6 $212.69   5.853%   $225.1387   $225.14   $225.15   $225.10  
  Purchase #7 $47.68   13.845%   $54.2813   $54.28   $54.30   $54.30  
  7 purchase totals = $884.99       $959.0561   $959.06   $959.10   $959.00