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 $145.46   3.860%   $151.0748   $151.07   $151.05   $151.10  
  Purchase #2 $203.31   4.546%   $212.5525   $212.55   $212.55   $212.60  
  Purchase #3 $36.42   8.804%   $39.6264   $39.63   $39.65   $39.60  
  Purchase #4 $106.47   7.613%   $114.5756   $114.58   $114.60   $114.60  
  Purchase #5 $49.39   7.215%   $52.9535   $52.95   $52.95   $53.00  
  Purchase #6 $185.73   11.227%   $206.5819   $206.58   $206.60   $206.60  
  Purchase #7 $169.27   5.496%   $178.5731   $178.57   $178.55   $178.60  
  7 purchase totals = $896.05       $955.9378   $955.93   $955.95   $956.10