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 $246.82   8.647%   $268.1625   $268.16   $268.15   $268.20  
  Purchase #2 $201.39   10.452%   $222.4393   $222.44   $222.45   $222.40  
  Purchase #3 $51.39   5.614%   $54.275   $54.28   $54.30   $54.30  
  Purchase #4 $39.55   5.660%   $41.7885   $41.79   $41.80   $41.80  
  Purchase #5 $128.81   6.702%   $137.4428   $137.44   $137.45   $137.40  
  Purchase #6 $129.38   4.318%   $134.9666   $134.97   $134.95   $135.00  
  Purchase #7 $55.79   11.631%   $62.2789   $62.28   $62.30   $62.30  
  7 purchase totals = $853.13       $921.3536   $921.36   $921.40   $921.40