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 $203.26   13.650%   $231.005   $231.01   $231.00   $231.00  
  Purchase #2 $175.54   9.160%   $191.6195   $191.62   $191.60   $191.60  
  Purchase #3 $79.48   11.627%   $88.7211   $88.72   $88.70   $88.70  
  Purchase #4 $27.81   11.185%   $30.9205   $30.92   $30.90   $30.90  
  Purchase #5 $140.82   13.663%   $160.0602   $160.06   $160.05   $160.10  
  Purchase #6 $66.87   10.670%   $74.005   $74.01   $74.00   $74.00  
  Purchase #7 $241.81   7.527%   $260.011   $260.01   $260.00   $260.00  
  7 purchase totals = $935.59       $1,036.3423   $1,036.35   $1,036.25   $1,036.30