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 $223.93   5.715%   $236.7276   $236.73   $236.75   $236.70  
  Purchase #2 $45.27   4.789%   $47.438   $47.44   $47.45   $47.40  
  Purchase #3 $60.61   7.718%   $65.2879   $65.29   $65.30   $65.30  
  Purchase #4 $115.97   4.639%   $121.3498   $121.35   $121.35   $121.30  
  Purchase #5 $229.54   6.616%   $244.7264   $244.73   $244.75   $244.70  
  Purchase #6 $21.72   5.501%   $22.9148   $22.91   $22.90   $22.90  
  Purchase #7 $247.40   10.858%   $274.2627   $274.26   $274.25   $274.30  
  7 purchase totals = $944.44       $1,012.7072   $1,012.71   $1,012.75   $1,012.60