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 $127.76   5.295%   $134.5249   $134.52   $134.50   $134.50  
  Purchase #2 $17.85   9.669%   $19.5759   $19.58   $19.60   $19.60  
  Purchase #3 $80.43   9.671%   $88.2084   $88.21   $88.20   $88.20  
  Purchase #4 $241.63   3.562%   $250.2369   $250.24   $250.25   $250.20  
  Purchase #5 $205.41   10.698%   $227.3848   $227.38   $227.40   $227.40  
  Purchase #6 $23.51   4.184%   $24.4937   $24.49   $24.50   $24.50  
  Purchase #7 $192.96   11.592%   $215.3279   $215.33   $215.35   $215.30  
  7 purchase totals = $889.55       $959.7525   $959.75   $959.80   $959.70