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 $126.74   8.519%   $137.537   $137.54   $137.55   $137.50  
  Purchase #2 $69.32   7.599%   $74.5876   $74.59   $74.60   $74.60  
  Purchase #3 $181.87   13.206%   $205.8878   $205.89   $205.90   $205.90  
  Purchase #4 $219.66   12.172%   $246.397   $246.40   $246.40   $246.40  
  Purchase #5 $239.95   5.702%   $253.6319   $253.63   $253.65   $253.60  
  Purchase #6 $221.99   13.769%   $252.5558   $252.56   $252.55   $252.60  
  Purchase #7 $155.60   5.138%   $163.5947   $163.59   $163.60   $163.60  
  7 purchase totals = $1,215.13       $1,334.1918   $1,334.20   $1,334.25   $1,334.20