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 $182.53   13.479%   $207.1332   $207.13   $207.15   $207.10  
  Purchase #2 $215.68   9.412%   $235.9798   $235.98   $236.00   $236.00  
  Purchase #3 $226.94   10.440%   $250.6325   $250.63   $250.65   $250.60  
  Purchase #4 $44.87   11.526%   $50.0417   $50.04   $50.05   $50.00  
  Purchase #5 $201.65   12.446%   $226.7474   $226.75   $226.75   $226.70  
  Purchase #6 $214.98   7.690%   $231.512   $231.51   $231.50   $231.50  
  Purchase #7 $75.87   6.614%   $80.888   $80.89   $80.90   $80.90  
  7 purchase totals = $1,162.52       $1,282.9346   $1,282.93   $1,283.00   $1,282.80