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 $235.53   13.698%   $267.7929   $267.79   $267.80   $267.80  
  Purchase #2 $113.48   5.138%   $119.3106   $119.31   $119.30   $119.30  
  Purchase #3 $167.37   5.147%   $175.9845   $175.98   $176.00   $176.00  
  Purchase #4 $69.34   3.710%   $71.9125   $71.91   $71.90   $71.90  
  Purchase #5 $129.91   8.740%   $141.2641   $141.26   $141.25   $141.30  
  Purchase #6 $71.75   5.496%   $75.6934   $75.69   $75.70   $75.70  
  Purchase #7 $182.62   4.714%   $191.2287   $191.23   $191.25   $191.20  
  7 purchase totals = $970.00       $1,043.1867   $1,043.17   $1,043.20   $1,043.20