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 $71.90   5.713%   $76.0076   $76.01   $76.00   $76.00  
  Purchase #2 $225.58   11.545%   $251.6232   $251.62   $251.60   $251.60  
  Purchase #3 $240.45   4.181%   $250.5032   $250.50   $250.50   $250.50  
  Purchase #4 $80.64   13.787%   $91.7578   $91.76   $91.75   $91.80  
  Purchase #5 $50.91   3.120%   $52.4984   $52.50   $52.50   $52.50  
  Purchase #6 $234.61   3.436%   $242.6712   $242.67   $242.65   $242.70  
  Purchase #7 $79.27   11.735%   $88.5723   $88.57   $88.55   $88.60  
  7 purchase totals = $983.36       $1,053.6337   $1,053.63   $1,053.55   $1,053.70