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 $248.93   7.179%   $266.8007   $266.80   $266.80   $266.80  
  Purchase #2 $218.97   10.324%   $241.5765   $241.58   $241.60   $241.60  
  Purchase #3 $80.48   4.262%   $83.9101   $83.91   $83.90   $83.90  
  Purchase #4 $18.89   11.587%   $21.0788   $21.08   $21.10   $21.10  
  Purchase #5 $119.27   9.554%   $130.6651   $130.67   $130.65   $130.70  
  Purchase #6 $95.62   12.502%   $107.5744   $107.57   $107.55   $107.60  
  Purchase #7 $30.90   7.491%   $33.2147   $33.21   $33.20   $33.20  
  7 purchase totals = $813.06       $884.8203   $884.82   $884.80   $884.90