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 $223.75   5.577%   $236.2285   $236.23   $236.25   $236.20  
  Purchase #2 $211.37   8.559%   $229.4612   $229.46   $229.45   $229.50  
  Purchase #3 $44.35   7.685%   $47.7583   $47.76   $47.75   $47.80  
  Purchase #4 $27.69   7.397%   $29.7382   $29.74   $29.75   $29.70  
  Purchase #5 $244.63   5.216%   $257.3899   $257.39   $257.40   $257.40  
  Purchase #6 $233.37   12.674%   $262.9473   $262.95   $262.95   $262.90  
  Purchase #7 $218.81   12.847%   $246.9205   $246.92   $246.90   $246.90  
  7 purchase totals = $1,203.97       $1,310.4439   $1,310.45   $1,310.45   $1,310.40