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 $58.99   8.686%   $64.1139   $64.11   $64.10   $64.10  
  Purchase #2 $111.91   7.150%   $119.9116   $119.91   $119.90   $119.90  
  Purchase #3 $238.93   12.133%   $267.9194   $267.92   $267.90   $267.90  
  Purchase #4 $153.91   4.525%   $160.8744   $160.87   $160.85   $160.90  
  Purchase #5 $126.66   11.717%   $141.5008   $141.50   $141.50   $141.50  
  Purchase #6 $160.73   9.430%   $175.8868   $175.89   $175.90   $175.90  
  Purchase #7 $66.63   7.739%   $71.7865   $71.79   $71.80   $71.80  
  7 purchase totals = $917.76       $1,001.9934   $1,001.99   $1,001.95   $1,002.00