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 $249.69   7.835%   $269.2532   $269.25   $269.25   $269.30  
  Purchase #2 $115.59   6.705%   $123.3403   $123.34   $123.35   $123.30  
  Purchase #3 $88.80   9.464%   $97.204   $97.20   $97.20   $97.20  
  Purchase #4 $196.87   4.846%   $206.4103   $206.41   $206.40   $206.40  
  Purchase #5 $217.91   5.395%   $229.6662   $229.67   $229.65   $229.70  
  Purchase #6 $62.73   11.756%   $70.1045   $70.10   $70.10   $70.10  
  Purchase #7 $246.31   3.239%   $254.288   $254.29   $254.30   $254.30  
  7 purchase totals = $1,177.90       $1,250.2665   $1,250.26   $1,250.25   $1,250.30