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 $30.49   6.106%   $32.3517   $32.35   $32.35   $32.40  
  Purchase #2 $202.54   11.539%   $225.9111   $225.91   $225.90   $225.90  
  Purchase #3 $144.92   11.774%   $161.9829   $161.98   $162.00   $162.00  
  Purchase #4 $132.32   8.508%   $143.5778   $143.58   $143.60   $143.60  
  Purchase #5 $202.69   9.258%   $221.455   $221.46   $221.45   $221.50  
  Purchase #6 $220.42   11.361%   $245.4619   $245.46   $245.45   $245.50  
  Purchase #7 $241.78   6.603%   $257.7447   $257.74   $257.75   $257.70  
  7 purchase totals = $1,175.16       $1,288.4851   $1,288.48   $1,288.50   $1,288.60