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 $188.49   10.801%   $208.8488   $208.85   $208.85   $208.80  
  Purchase #2 $119.95   5.227%   $126.2198   $126.22   $126.20   $126.20  
  Purchase #3 $47.47   10.297%   $52.358   $52.36   $52.35   $52.40  
  Purchase #4 $57.37   9.161%   $62.6257   $62.63   $62.65   $62.60  
  Purchase #5 $133.91   10.607%   $148.1138   $148.11   $148.10   $148.10  
  Purchase #6 $202.91   8.347%   $219.8469   $219.85   $219.85   $219.80  
  Purchase #7 $134.71   12.204%   $151.15   $151.15   $151.15   $151.20  
  7 purchase totals = $884.81       $969.1630   $969.17   $969.15   $969.10