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 $124.44   7.474%   $133.7406   $133.74   $133.75   $133.70  
  Purchase #2 $229.26   13.739%   $260.758   $260.76   $260.75   $260.80  
  Purchase #3 $88.81   9.139%   $96.9263   $96.93   $96.95   $96.90  
  Purchase #4 $181.98   6.365%   $193.563   $193.56   $193.55   $193.60  
  Purchase #5 $149.82   7.532%   $161.1044   $161.10   $161.10   $161.10  
  Purchase #6 $17.77   3.608%   $18.4111   $18.41   $18.40   $18.40  
  Purchase #7 $122.67   6.305%   $130.4043   $130.40   $130.40   $130.40  
  7 purchase totals = $914.75       $994.9077   $994.90   $994.90   $994.90