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 $214.76   12.110%   $240.7674   $240.77   $240.75   $240.80  
  Purchase #2 $244.55   3.474%   $253.0457   $253.05   $253.05   $253.00  
  Purchase #3 $25.42   4.785%   $26.6363   $26.64   $26.65   $26.60  
  Purchase #4 $140.97   5.592%   $148.853   $148.85   $148.85   $148.90  
  Purchase #5 $31.37   6.633%   $33.4508   $33.45   $33.45   $33.50  
  Purchase #6 $183.46   13.664%   $208.528   $208.53   $208.55   $208.50  
  Purchase #7 $135.29   12.192%   $151.7846   $151.78   $151.80   $151.80  
  7 purchase totals = $975.82       $1,063.0658   $1,063.07   $1,063.10   $1,063.10