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 $223.72   7.727%   $241.0068   $241.01   $241.00   $241.00  
  Purchase #2 $93.78   11.790%   $104.8367   $104.84   $104.85   $104.80  
  Purchase #3 $163.78   9.420%   $179.2081   $179.21   $179.20   $179.20  
  Purchase #4 $150.97   6.749%   $161.159   $161.16   $161.15   $161.20  
  Purchase #5 $234.54   11.824%   $262.272   $262.27   $262.25   $262.30  
  Purchase #6 $192.32   13.382%   $218.0563   $218.06   $218.05   $218.10  
  Purchase #7 $35.25   9.246%   $38.5092   $38.51   $38.50   $38.50  
  7 purchase totals = $1,094.36       $1,205.0481   $1,205.06   $1,205.00   $1,205.10