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 $34.61   10.248%   $38.1568   $38.16   $38.15   $38.20  
  Purchase #2 $218.46   9.702%   $239.655   $239.66   $239.65   $239.70  
  Purchase #3 $33.34   4.234%   $34.7516   $34.75   $34.75   $34.80  
  Purchase #4 $176.68   11.428%   $196.871   $196.87   $196.85   $196.90  
  Purchase #5 $219.54   7.437%   $235.8672   $235.87   $235.85   $235.90  
  Purchase #6 $216.39   11.176%   $240.5737   $240.57   $240.55   $240.60  
  Purchase #7 $218.92   9.779%   $240.3282   $240.33   $240.35   $240.30  
  7 purchase totals = $1,117.94       $1,226.2035   $1,226.21   $1,226.15   $1,226.40