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 $53.49   13.559%   $60.7427   $60.74   $60.75   $60.70  
  Purchase #2 $227.40   6.786%   $242.8314   $242.83   $242.85   $242.80  
  Purchase #3 $32.46   3.836%   $33.7052   $33.71   $33.70   $33.70  
  Purchase #4 $94.73   13.557%   $107.5725   $107.57   $107.55   $107.60  
  Purchase #5 $143.81   6.303%   $152.8743   $152.87   $152.85   $152.90  
  Purchase #6 $175.33   3.780%   $181.9575   $181.96   $181.95   $182.00  
  Purchase #7 $41.46   6.584%   $44.1897   $44.19   $44.20   $44.20  
  7 purchase totals = $768.68       $823.8733   $823.87   $823.85   $823.90