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 $66.69   13.647%   $75.7912   $75.79   $75.80   $75.80  
  Purchase #2 $161.30   11.355%   $179.6156   $179.62   $179.60   $179.60  
  Purchase #3 $72.34   13.548%   $82.1406   $82.14   $82.15   $82.10  
  Purchase #4 $68.33   3.168%   $70.4947   $70.49   $70.50   $70.50  
  Purchase #5 $176.70   13.850%   $201.173   $201.17   $201.15   $201.20  
  Purchase #6 $34.59   11.591%   $38.5993   $38.60   $38.60   $38.60  
  Purchase #7 $200.85   13.345%   $227.6534   $227.65   $227.65   $227.70  
  7 purchase totals = $780.80       $875.4678   $875.46   $875.45   $875.50