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 $57.99   8.253%   $62.7759   $62.78   $62.80   $62.80  
  Purchase #2 $170.35   3.135%   $175.6905   $175.69   $175.70   $175.70  
  Purchase #3 $78.88   9.448%   $86.3326   $86.33   $86.35   $86.30  
  Purchase #4 $218.38   4.312%   $227.7965   $227.80   $227.80   $227.80  
  Purchase #5 $50.33   11.556%   $56.1461   $56.15   $56.15   $56.10  
  Purchase #6 $107.52   8.147%   $116.2797   $116.28   $116.30   $116.30  
  Purchase #7 $203.97   13.745%   $232.0057   $232.01   $232.00   $232.00  
  7 purchase totals = $887.42       $957.0270   $957.04   $957.10   $957.00