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 $243.25   10.603%   $269.0418   $269.04   $269.05   $269.00  
  Purchase #2 $166.29   12.257%   $186.6722   $186.67   $186.65   $186.70  
  Purchase #3 $106.27   9.337%   $116.1924   $116.19   $116.20   $116.20  
  Purchase #4 $166.30   13.308%   $188.4312   $188.43   $188.45   $188.40  
  Purchase #5 $250.78   4.123%   $261.1197   $261.12   $261.10   $261.10  
  Purchase #6 $194.75   7.474%   $209.3056   $209.31   $209.30   $209.30  
  Purchase #7 $247.43   6.567%   $263.6787   $263.68   $263.70   $263.70  
  7 purchase totals = $1,375.07       $1,494.4416   $1,494.44   $1,494.45   $1,494.40