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 $67.44   5.794%   $71.3475   $71.35   $71.35   $71.30  
  Purchase #2 $101.33   6.311%   $107.7249   $107.72   $107.70   $107.70  
  Purchase #3 $214.71   6.871%   $229.4627   $229.46   $229.45   $229.50  
  Purchase #4 $217.93   11.733%   $243.4997   $243.50   $243.50   $243.50  
  Purchase #5 $49.41   10.574%   $54.6346   $54.63   $54.65   $54.60  
  Purchase #6 $230.39   10.261%   $254.0303   $254.03   $254.05   $254.00  
  Purchase #7 $141.38   3.678%   $146.58   $146.58   $146.60   $146.60  
  7 purchase totals = $1,022.59       $1,107.2797   $1,107.27   $1,107.30   $1,107.20