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 $235.53   10.643%   $260.5975   $260.60   $260.60   $260.60  
  Purchase #2 $236.97   9.138%   $258.6243   $258.62   $258.60   $258.60  
  Purchase #3 $212.53   9.345%   $232.3909   $232.39   $232.40   $232.40  
  Purchase #4 $51.83   8.850%   $56.417   $56.42   $56.40   $56.40  
  Purchase #5 $11.87   8.712%   $12.9041   $12.90   $12.90   $12.90  
  Purchase #6 $58.81   4.786%   $61.6246   $61.62   $61.60   $61.60  
  Purchase #7 $197.45   9.472%   $216.1525   $216.15   $216.15   $216.20  
  7 purchase totals = $1,004.99       $1,098.7109   $1,098.70   $1,098.65   $1,098.70