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 $98.58   8.461%   $106.9209   $106.92   $106.90   $106.90  
  Purchase #2 $81.58   5.834%   $86.3394   $86.34   $86.35   $86.30  
  Purchase #3 $61.26   5.686%   $64.7432   $64.74   $64.75   $64.70  
  Purchase #4 $201.33   12.690%   $226.8788   $226.88   $226.90   $226.90  
  Purchase #5 $140.35   13.793%   $159.7085   $159.71   $159.70   $159.70  
  Purchase #6 $218.99   3.852%   $227.4255   $227.43   $227.45   $227.40  
  Purchase #7 $135.94   13.843%   $154.7582   $154.76   $154.75   $154.80  
  7 purchase totals = $938.03       $1,026.7745   $1,026.78   $1,026.80   $1,026.70