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 $119.61   12.513%   $134.5768   $134.58   $134.60   $134.60  
  Purchase #2 $83.82   8.676%   $91.0922   $91.09   $91.10   $91.10  
  Purchase #3 $186.49   4.336%   $194.5762   $194.58   $194.60   $194.60  
  Purchase #4 $177.49   4.352%   $185.2144   $185.21   $185.20   $185.20  
  Purchase #5 $244.76   10.290%   $269.9458   $269.95   $269.95   $269.90  
  Purchase #6 $133.95   3.684%   $138.8847   $138.88   $138.90   $138.90  
  Purchase #7 $234.50   5.313%   $246.959   $246.96   $246.95   $247.00  
  7 purchase totals = $1,180.62       $1,261.2491   $1,261.25   $1,261.30   $1,261.30