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 $63.81   6.197%   $67.7643   $67.76   $67.75   $67.80  
  Purchase #2 $233.95   9.798%   $256.8724   $256.87   $256.85   $256.90  
  Purchase #3 $23.27   12.610%   $26.2043   $26.20   $26.20   $26.20  
  Purchase #4 $51.53   12.477%   $57.9594   $57.96   $57.95   $58.00  
  Purchase #5 $154.29   8.113%   $166.8075   $166.81   $166.80   $166.80  
  Purchase #6 $153.86   6.215%   $163.4224   $163.42   $163.40   $163.40  
  Purchase #7 $167.84   11.503%   $187.1466   $187.15   $187.15   $187.10  
  7 purchase totals = $848.55       $926.1769   $926.17   $926.10   $926.20