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 $217.49   4.795%   $227.9186   $227.92   $227.90   $227.90  
  Purchase #2 $125.44   11.860%   $140.3172   $140.32   $140.30   $140.30  
  Purchase #3 $47.52   7.851%   $51.2508   $51.25   $51.25   $51.30  
  Purchase #4 $105.92   4.681%   $110.8781   $110.88   $110.90   $110.90  
  Purchase #5 $35.44   11.815%   $39.6272   $39.63   $39.65   $39.60  
  Purchase #6 $229.58   3.768%   $238.2306   $238.23   $238.25   $238.20  
  Purchase #7 $200.93   7.255%   $215.5075   $215.51   $215.50   $215.50  
  7 purchase totals = $962.32       $1,023.7300   $1,023.74   $1,023.75   $1,023.70