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 $76.54   12.433%   $86.0562   $86.06   $86.05   $86.10  
  Purchase #2 $151.97   11.108%   $168.8508   $168.85   $168.85   $168.90  
  Purchase #3 $164.42   11.460%   $183.2625   $183.26   $183.25   $183.30  
  Purchase #4 $66.89   9.633%   $73.3335   $73.33   $73.35   $73.30  
  Purchase #5 $219.65   8.628%   $238.6014   $238.60   $238.60   $238.60  
  Purchase #6 $21.52   13.743%   $24.4775   $24.48   $24.50   $24.50  
  Purchase #7 $70.28   4.369%   $73.3505   $73.35   $73.35   $73.40  
  7 purchase totals = $771.27       $847.9324   $847.93   $847.95   $848.10