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 $25.82   3.543%   $26.7348   $26.73   $26.75   $26.70  
  Purchase #2 $67.98   10.258%   $74.9534   $74.95   $74.95   $75.00  
  Purchase #3 $165.58   7.548%   $178.078   $178.08   $178.10   $178.10  
  Purchase #4 $93.52   8.769%   $101.7208   $101.72   $101.70   $101.70  
  Purchase #5 $20.62   9.402%   $22.5587   $22.56   $22.55   $22.60  
  Purchase #6 $83.36   11.380%   $92.8464   $92.85   $92.85   $92.80  
  Purchase #7 $47.25   8.678%   $51.3504   $51.35   $51.35   $51.40  
  7 purchase totals = $504.13       $548.2425   $548.24   $548.25   $548.30