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 $183.67   13.770%   $208.9614   $208.96   $208.95   $209.00  
  Purchase #2 $33.89   12.599%   $38.1598   $38.16   $38.15   $38.20  
  Purchase #3 $16.46   3.470%   $17.0312   $17.03   $17.05   $17.00  
  Purchase #4 $220.25   7.273%   $236.2688   $236.27   $236.25   $236.30  
  Purchase #5 $134.77   13.282%   $152.6702   $152.67   $152.65   $152.70  
  Purchase #6 $186.80   6.603%   $199.1344   $199.13   $199.15   $199.10  
  Purchase #7 $186.83   9.464%   $204.5116   $204.51   $204.50   $204.50  
  7 purchase totals = $962.67       $1,056.7374   $1,056.73   $1,056.70   $1,056.80