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 $245.88   11.700%   $274.648   $274.65   $274.65   $274.60  
  Purchase #2 $107.88   3.736%   $111.9104   $111.91   $111.90   $111.90  
  Purchase #3 $25.26   5.277%   $26.593   $26.59   $26.60   $26.60  
  Purchase #4 $235.65   3.439%   $243.754   $243.75   $243.75   $243.80  
  Purchase #5 $41.55   4.172%   $43.2835   $43.28   $43.30   $43.30  
  Purchase #6 $96.66   5.402%   $101.8816   $101.88   $101.90   $101.90  
  Purchase #7 $75.79   13.678%   $86.1566   $86.16   $86.15   $86.20  
  7 purchase totals = $828.67       $888.2271   $888.22   $888.25   $888.30