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 $104.83   13.777%   $119.2724   $119.27   $119.25   $119.30  
  Purchase #2 $161.54   9.566%   $176.9929   $176.99   $177.00   $177.00  
  Purchase #3 $201.28   9.709%   $220.8223   $220.82   $220.80   $220.80  
  Purchase #4 $119.35   11.234%   $132.7578   $132.76   $132.75   $132.80  
  Purchase #5 $126.70   8.745%   $137.7799   $137.78   $137.80   $137.80  
  Purchase #6 $163.36   9.498%   $178.8759   $178.88   $178.90   $178.90  
  Purchase #7 $216.98   9.278%   $237.1114   $237.11   $237.10   $237.10  
  7 purchase totals = $1,094.04       $1,203.6126   $1,203.61   $1,203.60   $1,203.70