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 $91.51   5.465%   $96.511   $96.51   $96.50   $96.50  
  Purchase #2 $187.77   13.257%   $212.6627   $212.66   $212.65   $212.70  
  Purchase #3 $76.97   11.846%   $86.0879   $86.09   $86.10   $86.10  
  Purchase #4 $24.61   10.527%   $27.2007   $27.20   $27.20   $27.20  
  Purchase #5 $129.61   13.861%   $147.5752   $147.58   $147.60   $147.60  
  Purchase #6 $73.70   11.224%   $81.9721   $81.97   $81.95   $82.00  
  Purchase #7 $63.98   3.730%   $66.3665   $66.37   $66.35   $66.40  
  7 purchase totals = $648.15       $718.3761   $718.38   $718.35   $718.50