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 $208.43   12.869%   $235.2529   $235.25   $235.25   $235.30  
  Purchase #2 $245.37   12.502%   $276.0462   $276.05   $276.05   $276.00  
  Purchase #3 $67.29   3.388%   $69.5698   $69.57   $69.55   $69.60  
  Purchase #4 $93.69   7.559%   $100.772   $100.77   $100.75   $100.80  
  Purchase #5 $208.55   6.152%   $221.38   $221.38   $221.40   $221.40  
  Purchase #6 $58.47   8.293%   $63.3189   $63.32   $63.30   $63.30  
  Purchase #7 $216.87   12.675%   $244.3583   $244.36   $244.35   $244.40  
  7 purchase totals = $1,098.67       $1,210.6981   $1,210.70   $1,210.65   $1,210.80