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 $204.96   9.266%   $223.9516   $223.95   $223.95   $224.00  
  Purchase #2 $124.78   12.248%   $140.0631   $140.06   $140.05   $140.10  
  Purchase #3 $155.88   10.701%   $172.5607   $172.56   $172.55   $172.60  
  Purchase #4 $182.69   8.350%   $197.9446   $197.94   $197.95   $197.90  
  Purchase #5 $173.42   11.297%   $193.0113   $193.01   $193.00   $193.00  
  Purchase #6 $203.36   9.621%   $222.9253   $222.93   $222.95   $222.90  
  Purchase #7 $67.68   7.103%   $72.4873   $72.49   $72.50   $72.50  
  7 purchase totals = $1,112.77       $1,222.9439   $1,222.94   $1,222.95   $1,223.00