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 $171.92   6.136%   $182.469   $182.47   $182.45   $182.50  
  Purchase #2 $58.74   12.395%   $66.0208   $66.02   $66.00   $66.00  
  Purchase #3 $163.62   3.202%   $168.8591   $168.86   $168.85   $168.90  
  Purchase #4 $61.96   5.307%   $65.2482   $65.25   $65.25   $65.20  
  Purchase #5 $82.57   9.678%   $90.5611   $90.56   $90.55   $90.60  
  Purchase #6 $201.40   10.359%   $222.263   $222.26   $222.25   $222.30  
  Purchase #7 $219.85   3.707%   $227.9998   $228.00   $228.00   $228.00  
  7 purchase totals = $960.06       $1,023.4210   $1,023.42   $1,023.35   $1,023.50