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 $98.55   8.598%   $107.0233   $107.02   $107.00   $107.00  
  Purchase #2 $227.60   7.127%   $243.8211   $243.82   $243.80   $243.80  
  Purchase #3 $25.34   3.406%   $26.2031   $26.20   $26.20   $26.20  
  Purchase #4 $191.57   9.658%   $210.0718   $210.07   $210.05   $210.10  
  Purchase #5 $8.43   8.673%   $9.1611   $9.16   $9.15   $9.20  
  Purchase #6 $116.42   11.200%   $129.459   $129.46   $129.45   $129.50  
  Purchase #7 $232.66   11.412%   $259.2112   $259.21   $259.20   $259.20  
  7 purchase totals = $900.57       $984.9506   $984.94   $984.85   $985.00