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 $191.68   13.192%   $216.9664   $216.97   $216.95   $217.00  
  Purchase #2 $238.62   12.442%   $268.3091   $268.31   $268.30   $268.30  
  Purchase #3 $224.71   6.463%   $239.233   $239.23   $239.25   $239.20  
  Purchase #4 $190.42   4.131%   $198.2863   $198.29   $198.30   $198.30  
  Purchase #5 $8.91   12.191%   $9.9962   $10.00   $10.00   $10.00  
  Purchase #6 $229.55   7.165%   $245.9973   $246.00   $246.00   $246.00  
  Purchase #7 $66.76   4.760%   $69.9378   $69.94   $69.95   $69.90  
  7 purchase totals = $1,150.65       $1,248.7261   $1,248.74   $1,248.75   $1,248.70