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 $242.75   8.746%   $263.9809   $263.98   $264.00   $264.00  
  Purchase #2 $111.97   13.441%   $127.0199   $127.02   $127.00   $127.00  
  Purchase #3 $38.79   6.384%   $41.2664   $41.27   $41.25   $41.30  
  Purchase #4 $55.63   12.252%   $62.4458   $62.45   $62.45   $62.40  
  Purchase #5 $247.36   8.689%   $268.8531   $268.85   $268.85   $268.90  
  Purchase #6 $138.74   11.443%   $154.616   $154.62   $154.60   $154.60  
  Purchase #7 $188.26   3.830%   $195.4704   $195.47   $195.45   $195.50  
  7 purchase totals = $1,023.50       $1,113.6525   $1,113.66   $1,113.60   $1,113.70