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 $22.28   10.859%   $24.6994   $24.70   $24.70   $24.70  
  Purchase #2 $225.76   3.489%   $233.6368   $233.64   $233.65   $233.60  
  Purchase #3 $121.67   6.303%   $129.3389   $129.34   $129.35   $129.30  
  Purchase #4 $11.46   3.464%   $11.857   $11.86   $11.85   $11.90  
  Purchase #5 $83.66   5.467%   $88.2337   $88.23   $88.25   $88.20  
  Purchase #6 $187.38   13.157%   $212.0336   $212.03   $212.05   $212.00  
  Purchase #7 $34.47   4.368%   $35.9756   $35.98   $36.00   $36.00  
  7 purchase totals = $686.68       $735.7750   $735.78   $735.85   $735.70