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 $143.76   7.545%   $154.6067   $154.61   $154.60   $154.60  
  Purchase #2 $241.94   10.731%   $267.9026   $267.90   $267.90   $267.90  
  Purchase #3 $206.77   13.722%   $235.143   $235.14   $235.15   $235.10  
  Purchase #4 $112.61   5.750%   $119.0851   $119.09   $119.10   $119.10  
  Purchase #5 $248.63   9.462%   $272.1554   $272.16   $272.15   $272.20  
  Purchase #6 $115.90   12.685%   $130.6019   $130.60   $130.60   $130.60  
  Purchase #7 $65.88   8.323%   $71.3632   $71.36   $71.35   $71.40  
  7 purchase totals = $1,135.49       $1,250.8579   $1,250.86   $1,250.85   $1,250.90