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 $242.58   7.208%   $260.0652   $260.07   $260.05   $260.10  
  Purchase #2 $211.89   10.411%   $233.9499   $233.95   $233.95   $233.90  
  Purchase #3 $117.47   5.469%   $123.8944   $123.89   $123.90   $123.90  
  Purchase #4 $153.96   10.197%   $169.6593   $169.66   $169.65   $169.70  
  Purchase #5 $165.71   7.345%   $177.8814   $177.88   $177.90   $177.90  
  Purchase #6 $206.63   8.381%   $223.9477   $223.95   $223.95   $223.90  
  Purchase #7 $33.95   9.361%   $37.1281   $37.13   $37.15   $37.10  
  7 purchase totals = $1,132.19       $1,226.5260   $1,226.53   $1,226.55   $1,226.50