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 $84.97   11.286%   $94.5597   $94.56   $94.55   $94.60  
  Purchase #2 $221.92   7.239%   $237.9848   $237.98   $238.00   $238.00  
  Purchase #3 $58.31   11.714%   $65.1404   $65.14   $65.15   $65.10  
  Purchase #4 $137.83   7.723%   $148.4746   $148.47   $148.45   $148.50  
  Purchase #5 $87.29   13.652%   $99.2068   $99.21   $99.20   $99.20  
  Purchase #6 $194.25   13.555%   $220.5806   $220.58   $220.60   $220.60  
  Purchase #7 $79.95   8.131%   $86.4507   $86.45   $86.45   $86.50  
  7 purchase totals = $864.52       $952.3976   $952.39   $952.40   $952.50