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 $242.39   10.834%   $268.6505   $268.65   $268.65   $268.70  
  Purchase #2 $72.66   11.293%   $80.8655   $80.87   $80.85   $80.90  
  Purchase #3 $121.83   9.722%   $133.6743   $133.67   $133.65   $133.70  
  Purchase #4 $54.57   5.621%   $57.6374   $57.64   $57.65   $57.60  
  Purchase #5 $163.92   9.689%   $179.8022   $179.80   $179.80   $179.80  
  Purchase #6 $132.76   9.189%   $144.9593   $144.96   $144.95   $145.00  
  Purchase #7 $168.42   7.622%   $181.257   $181.26   $181.25   $181.30  
  7 purchase totals = $956.55       $1,046.8462   $1,046.85   $1,046.80   $1,047.00