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 $86.65   13.623%   $98.4543   $98.45   $98.45   $98.50  
  Purchase #2 $211.66   9.633%   $232.0492   $232.05   $232.05   $232.00  
  Purchase #3 $139.44   12.225%   $156.4865   $156.49   $156.50   $156.50  
  Purchase #4 $23.98   8.471%   $26.0113   $26.01   $26.00   $26.00  
  Purchase #5 $192.36   12.845%   $217.0686   $217.07   $217.05   $217.10  
  Purchase #6 $227.26   13.167%   $257.1833   $257.18   $257.20   $257.20  
  Purchase #7 $63.62   4.280%   $66.3429   $66.34   $66.35   $66.30  
  7 purchase totals = $944.97       $1,053.5961   $1,053.59   $1,053.60   $1,053.60