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 $198.76   13.214%   $225.0241   $225.02   $225.00   $225.00  
  Purchase #2 $157.50   9.381%   $172.2751   $172.28   $172.30   $172.30  
  Purchase #3 $203.97   11.536%   $227.5   $227.50   $227.50   $227.50  
  Purchase #4 $244.58   9.428%   $267.639   $267.64   $267.65   $267.60  
  Purchase #5 $242.55   6.806%   $259.058   $259.06   $259.05   $259.10  
  Purchase #6 $167.59   5.604%   $176.9817   $176.98   $177.00   $177.00  
  Purchase #7 $116.30   13.105%   $131.5411   $131.54   $131.55   $131.50  
  7 purchase totals = $1,331.25       $1,460.0190   $1,460.02   $1,460.05   $1,460.00