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 $118.27   7.268%   $126.8659   $126.87   $126.85   $126.90  
  Purchase #2 $167.71   10.262%   $184.9204   $184.92   $184.90   $184.90  
  Purchase #3 $229.99   4.613%   $240.5994   $240.60   $240.60   $240.60  
  Purchase #4 $182.63   11.124%   $202.9458   $202.95   $202.95   $202.90  
  Purchase #5 $127.64   3.688%   $132.3474   $132.35   $132.35   $132.30  
  Purchase #6 $43.56   4.448%   $45.4975   $45.50   $45.50   $45.50  
  Purchase #7 $179.74   3.493%   $186.0183   $186.02   $186.00   $186.00  
  7 purchase totals = $1,049.54       $1,119.1947   $1,119.21   $1,119.15   $1,119.10