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 $118.74   8.298%   $128.593   $128.59   $128.60   $128.60  
  Purchase #2 $230.43   10.513%   $254.6551   $254.66   $254.65   $254.70  
  Purchase #3 $17.47   13.621%   $19.8496   $19.85   $19.85   $19.80  
  Purchase #4 $228.58   8.751%   $248.583   $248.58   $248.60   $248.60  
  Purchase #5 $94.55   3.783%   $98.1268   $98.13   $98.15   $98.10  
  Purchase #6 $184.50   9.793%   $202.5681   $202.57   $202.55   $202.60  
  Purchase #7 $167.76   13.620%   $190.6089   $190.61   $190.60   $190.60  
  7 purchase totals = $1,042.03       $1,142.9845   $1,142.99   $1,143.00   $1,143.00