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 $208.44   11.791%   $233.0172   $233.02   $233.00   $233.00  
  Purchase #2 $55.78   12.584%   $62.7994   $62.80   $62.80   $62.80  
  Purchase #3 $151.51   13.540%   $172.0245   $172.02   $172.00   $172.00  
  Purchase #4 $75.95   7.292%   $81.4883   $81.49   $81.50   $81.50  
  Purchase #5 $237.48   6.500%   $252.9162   $252.92   $252.90   $252.90  
  Purchase #6 $140.96   8.173%   $152.4807   $152.48   $152.50   $152.50  
  Purchase #7 $13.45   6.724%   $14.3544   $14.35   $14.35   $14.40  
  7 purchase totals = $883.57       $969.0807   $969.08   $969.05   $969.10