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 $196.32   7.489%   $211.0224   $211.02   $211.00   $211.00  
  Purchase #2 $171.88   4.579%   $179.7504   $179.75   $179.75   $179.80  
  Purchase #3 $53.48   13.870%   $60.8977   $60.90   $60.90   $60.90  
  Purchase #4 $49.93   5.462%   $52.6572   $52.66   $52.65   $52.70  
  Purchase #5 $166.83   13.441%   $189.2536   $189.25   $189.25   $189.30  
  Purchase #6 $47.90   11.664%   $53.4871   $53.49   $53.50   $53.50  
  Purchase #7 $124.27   9.261%   $135.7786   $135.78   $135.80   $135.80  
  7 purchase totals = $810.61       $882.8470   $882.85   $882.85   $883.00