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 $232.56   11.812%   $260.03   $260.03   $260.05   $260.00  
  Purchase #2 $153.62   13.720%   $174.6967   $174.70   $174.70   $174.70  
  Purchase #3 $180.60   5.658%   $190.8183   $190.82   $190.80   $190.80  
  Purchase #4 $104.28   5.716%   $110.2406   $110.24   $110.25   $110.20  
  Purchase #5 $195.86   9.604%   $214.6704   $214.67   $214.65   $214.70  
  Purchase #6 $194.77   5.383%   $205.2545   $205.25   $205.25   $205.30  
  Purchase #7 $141.31   11.776%   $157.9507   $157.95   $157.95   $158.00  
  7 purchase totals = $1,203.00       $1,313.6612   $1,313.66   $1,313.65   $1,313.70