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 $163.30   13.256%   $184.947   $184.95   $184.95   $184.90  
  Purchase #2 $56.83   6.862%   $60.7297   $60.73   $60.75   $60.70  
  Purchase #3 $76.37   13.635%   $86.783   $86.78   $86.80   $86.80  
  Purchase #4 $48.34   9.580%   $52.971   $52.97   $52.95   $53.00  
  Purchase #5 $128.93   11.530%   $143.7956   $143.80   $143.80   $143.80  
  Purchase #6 $239.34   5.482%   $252.4606   $252.46   $252.45   $252.50  
  Purchase #7 $168.82   4.227%   $175.956   $175.96   $175.95   $176.00  
  7 purchase totals = $881.93       $957.6429   $957.65   $957.65   $957.70