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 $116.61   7.240%   $125.0526   $125.05   $125.05   $125.10  
  Purchase #2 $89.51   5.289%   $94.2442   $94.24   $94.25   $94.20  
  Purchase #3 $104.48   3.249%   $107.8746   $107.87   $107.85   $107.90  
  Purchase #4 $171.44   3.617%   $177.641   $177.64   $177.65   $177.60  
  Purchase #5 $88.78   5.805%   $93.9337   $93.93   $93.95   $93.90  
  Purchase #6 $219.48   7.418%   $235.761   $235.76   $235.75   $235.80  
  Purchase #7 $185.77   4.696%   $194.4938   $194.49   $194.50   $194.50  
  7 purchase totals = $976.07       $1,029.0009   $1,028.98   $1,029.00   $1,029.00