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 $244.74   8.611%   $265.8146   $265.81   $265.80   $265.80  
  Purchase #2 $48.87   3.204%   $50.4358   $50.44   $50.45   $50.40  
  Purchase #3 $231.54   8.743%   $251.7835   $251.78   $251.80   $251.80  
  Purchase #4 $245.91   3.610%   $254.7874   $254.79   $254.80   $254.80  
  Purchase #5 $132.80   10.492%   $146.7334   $146.73   $146.75   $146.70  
  Purchase #6 $131.71   8.364%   $142.7262   $142.73   $142.75   $142.70  
  Purchase #7 $133.79   10.437%   $147.7537   $147.75   $147.75   $147.80  
  7 purchase totals = $1,169.36       $1,260.0346   $1,260.03   $1,260.10   $1,260.00