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 $60.48   10.112%   $66.5957   $66.60   $66.60   $66.60  
  Purchase #2 $41.44   12.374%   $46.5678   $46.57   $46.55   $46.60  
  Purchase #3 $95.80   12.609%   $107.8794   $107.88   $107.90   $107.90  
  Purchase #4 $173.42   5.144%   $182.3407   $182.34   $182.35   $182.30  
  Purchase #5 $227.82   6.651%   $242.9723   $242.97   $242.95   $243.00  
  Purchase #6 $128.76   12.267%   $144.555   $144.56   $144.55   $144.60  
  Purchase #7 $195.86   11.665%   $218.7071   $218.71   $218.70   $218.70  
  7 purchase totals = $923.58       $1,009.6180   $1,009.63   $1,009.60   $1,009.70