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 $242.79   4.217%   $253.0285   $253.03   $253.05   $253.00  
  Purchase #2 $131.74   3.193%   $135.9465   $135.95   $135.95   $135.90  
  Purchase #3 $28.60   12.408%   $32.1487   $32.15   $32.15   $32.10  
  Purchase #4 $196.37   12.438%   $220.7945   $220.79   $220.80   $220.80  
  Purchase #5 $217.43   12.713%   $245.0719   $245.07   $245.05   $245.10  
  Purchase #6 $117.73   11.658%   $131.455   $131.46   $131.45   $131.50  
  Purchase #7 $228.31   8.145%   $246.9058   $246.91   $246.90   $246.90  
  7 purchase totals = $1,162.97       $1,265.3509   $1,265.36   $1,265.35   $1,265.30