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 $164.78   11.372%   $183.5188   $183.52   $183.50   $183.50  
  Purchase #2 $164.41   8.774%   $178.8353   $178.84   $178.85   $178.80  
  Purchase #3 $45.99   13.652%   $52.2686   $52.27   $52.25   $52.30  
  Purchase #4 $90.54   3.786%   $93.9678   $93.97   $93.95   $94.00  
  Purchase #5 $213.99   5.330%   $225.3957   $225.40   $225.40   $225.40  
  Purchase #6 $57.95   6.844%   $61.9161   $61.92   $61.90   $61.90  
  Purchase #7 $57.66   12.155%   $64.6686   $64.67   $64.65   $64.70  
  7 purchase totals = $795.32       $860.5709   $860.59   $860.50   $860.60