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 $61.86   12.753%   $69.749   $69.75   $69.75   $69.70  
  Purchase #2 $96.44   3.311%   $99.6331   $99.63   $99.65   $99.60  
  Purchase #3 $176.80   10.412%   $195.2084   $195.21   $195.20   $195.20  
  Purchase #4 $141.31   7.137%   $151.3953   $151.40   $151.40   $151.40  
  Purchase #5 $188.83   10.601%   $208.8479   $208.85   $208.85   $208.80  
  Purchase #6 $209.27   4.780%   $219.2731   $219.27   $219.25   $219.30  
  Purchase #7 $15.79   12.394%   $17.747   $17.75   $17.75   $17.70  
  7 purchase totals = $890.30       $961.8538   $961.86   $961.85   $961.70