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 $86.62   13.342%   $98.1768   $98.18   $98.20   $98.20  
  Purchase #2 $185.36   4.430%   $193.5714   $193.57   $193.55   $193.60  
  Purchase #3 $248.67   12.450%   $279.6294   $279.63   $279.65   $279.60  
  Purchase #4 $197.58   10.789%   $218.8969   $218.90   $218.90   $218.90  
  Purchase #5 $27.58   13.768%   $31.3772   $31.38   $31.40   $31.40  
  Purchase #6 $163.37   8.858%   $177.8413   $177.84   $177.85   $177.80  
  Purchase #7 $49.92   13.474%   $56.6462   $56.65   $56.65   $56.60  
  7 purchase totals = $959.10       $1,056.1392   $1,056.15   $1,056.20   $1,056.10