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 $208.77   11.874%   $233.5593   $233.56   $233.55   $233.60  
  Purchase #2 $175.27   7.348%   $188.1488   $188.15   $188.15   $188.10  
  Purchase #3 $38.88   7.103%   $41.6416   $41.64   $41.65   $41.60  
  Purchase #4 $223.91   4.261%   $233.4508   $233.45   $233.45   $233.50  
  Purchase #5 $201.67   12.200%   $226.2737   $226.27   $226.25   $226.30  
  Purchase #6 $220.87   13.817%   $251.3876   $251.39   $251.40   $251.40  
  Purchase #7 $88.53   6.259%   $94.0711   $94.07   $94.05   $94.10  
  7 purchase totals = $1,157.90       $1,268.5329   $1,268.53   $1,268.50   $1,268.60