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 $221.84   11.687%   $247.7664   $247.77   $247.75   $247.80  
  Purchase #2 $216.94   4.413%   $226.5136   $226.51   $226.50   $226.50  
  Purchase #3 $232.48   10.258%   $256.3278   $256.33   $256.35   $256.30  
  Purchase #4 $83.79   3.679%   $86.8726   $86.87   $86.85   $86.90  
  Purchase #5 $240.70   3.656%   $249.5   $249.50   $249.50   $249.50  
  Purchase #6 $67.72   12.798%   $76.3868   $76.39   $76.40   $76.40  
  Purchase #7 $203.72   11.870%   $227.9016   $227.90   $227.90   $227.90  
  7 purchase totals = $1,267.19       $1,371.2688   $1,371.27   $1,371.25   $1,371.30