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 $67.27   4.547%   $70.3288   $70.33   $70.35   $70.30  
  Purchase #2 $181.63   11.548%   $202.6046   $202.60   $202.60   $202.60  
  Purchase #3 $13.67   11.454%   $15.2358   $15.24   $15.25   $15.20  
  Purchase #4 $21.92   12.817%   $24.7295   $24.73   $24.75   $24.70  
  Purchase #5 $60.25   6.711%   $64.2934   $64.29   $64.30   $64.30  
  Purchase #6 $165.62   11.624%   $184.8717   $184.87   $184.85   $184.90  
  Purchase #7 $170.66   6.420%   $181.6164   $181.62   $181.60   $181.60  
  7 purchase totals = $681.02       $743.6802   $743.68   $743.70   $743.60