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 $220.98   11.681%   $246.7927   $246.79   $246.80   $246.80  
  Purchase #2 $248.65   4.147%   $258.9615   $258.96   $258.95   $259.00  
  Purchase #3 $166.33   10.378%   $183.5917   $183.59   $183.60   $183.60  
  Purchase #4 $32.53   6.346%   $34.5944   $34.59   $34.60   $34.60  
  Purchase #5 $95.90   13.521%   $108.8666   $108.87   $108.85   $108.90  
  Purchase #6 $106.48   9.464%   $116.5573   $116.56   $116.55   $116.60  
  Purchase #7 $107.41   10.334%   $118.5097   $118.51   $118.50   $118.50  
  7 purchase totals = $978.28       $1,067.8739   $1,067.87   $1,067.85   $1,068.00