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 $101.91   12.414%   $114.5611   $114.56   $114.55   $114.60  
  Purchase #2 $48.71   6.838%   $52.0408   $52.04   $52.05   $52.00  
  Purchase #3 $152.61   11.517%   $170.1861   $170.19   $170.20   $170.20  
  Purchase #4 $174.54   9.256%   $190.6954   $190.70   $190.70   $190.70  
  Purchase #5 $185.65   3.697%   $192.5135   $192.51   $192.50   $192.50  
  Purchase #6 $79.54   9.590%   $87.1679   $87.17   $87.15   $87.20  
  Purchase #7 $148.74   13.568%   $168.921   $168.92   $168.90   $168.90  
  7 purchase totals = $891.70       $976.0858   $976.09   $976.05   $976.10