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 $82.97   4.366%   $86.5925   $86.59   $86.60   $86.60  
  Purchase #2 $186.84   12.314%   $209.8475   $209.85   $209.85   $209.80  
  Purchase #3 $52.72   6.205%   $55.9913   $55.99   $56.00   $56.00  
  Purchase #4 $234.91   12.548%   $264.3865   $264.39   $264.40   $264.40  
  Purchase #5 $56.97   11.609%   $63.5836   $63.58   $63.60   $63.60  
  Purchase #6 $109.61   13.833%   $124.7724   $124.77   $124.75   $124.80  
  Purchase #7 $213.79   13.638%   $242.9467   $242.95   $242.95   $242.90  
  7 purchase totals = $937.81       $1,048.1205   $1,048.12   $1,048.15   $1,048.10