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 $208.65   12.398%   $234.5184   $234.52   $234.50   $234.50  
  Purchase #2 $90.54   5.365%   $95.3975   $95.40   $95.40   $95.40  
  Purchase #3 $144.25   13.687%   $163.9935   $163.99   $164.00   $164.00  
  Purchase #4 $107.83   7.281%   $115.6811   $115.68   $115.70   $115.70  
  Purchase #5 $50.29   7.173%   $53.8973   $53.90   $53.90   $53.90  
  Purchase #6 $180.85   11.574%   $201.7816   $201.78   $201.80   $201.80  
  Purchase #7 $216.28   9.313%   $236.4222   $236.42   $236.40   $236.40  
  7 purchase totals = $998.69       $1,101.6916   $1,101.69   $1,101.70   $1,101.70