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 $211.28   6.513%   $225.0407   $225.04   $225.05   $225.00  
  Purchase #2 $52.41   11.446%   $58.4088   $58.41   $58.40   $58.40  
  Purchase #3 $86.85   10.547%   $96.0101   $96.01   $96.00   $96.00  
  Purchase #4 $152.59   5.661%   $161.2281   $161.23   $161.25   $161.20  
  Purchase #5 $67.43   8.495%   $73.1582   $73.16   $73.15   $73.20  
  Purchase #6 $202.62   6.832%   $216.463   $216.46   $216.45   $216.50  
  Purchase #7 $56.49   10.711%   $62.5406   $62.54   $62.55   $62.50  
  7 purchase totals = $829.67       $892.8495   $892.85   $892.85   $892.80