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 $60.33   13.133%   $68.2531   $68.25   $68.25   $68.30  
  Purchase #2 $11.42   5.647%   $12.0649   $12.06   $12.05   $12.10  
  Purchase #3 $148.36   9.115%   $161.883   $161.88   $161.90   $161.90  
  Purchase #4 $246.86   5.558%   $260.5805   $260.58   $260.60   $260.60  
  Purchase #5 $175.69   11.162%   $195.3005   $195.30   $195.30   $195.30  
  Purchase #6 $12.44   6.181%   $13.2089   $13.21   $13.20   $13.20  
  Purchase #7 $107.86   13.280%   $122.1838   $122.18   $122.20   $122.20  
  7 purchase totals = $762.96       $833.4747   $833.46   $833.50   $833.60