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 $115.50   6.569%   $123.0872   $123.09   $123.10   $123.10  
  Purchase #2 $200.87   3.714%   $208.3303   $208.33   $208.35   $208.30  
  Purchase #3 $127.29   6.442%   $135.49   $135.49   $135.50   $135.50  
  Purchase #4 $234.27   6.120%   $248.6073   $248.61   $248.60   $248.60  
  Purchase #5 $207.89   13.306%   $235.5518   $235.55   $235.55   $235.60  
  Purchase #6 $211.95   6.262%   $225.2223   $225.22   $225.20   $225.20  
  Purchase #7 $247.71   12.348%   $278.2972   $278.30   $278.30   $278.30  
  7 purchase totals = $1,345.48       $1,454.5861   $1,454.59   $1,454.60   $1,454.60