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 $87.61   8.165%   $94.7634   $94.76   $94.75   $94.80  
  Purchase #2 $196.57   3.802%   $204.0436   $204.04   $204.05   $204.00  
  Purchase #3 $232.64   6.259%   $247.2009   $247.20   $247.20   $247.20  
  Purchase #4 $39.27   12.337%   $44.1147   $44.11   $44.10   $44.10  
  Purchase #5 $232.37   7.405%   $249.577   $249.58   $249.60   $249.60  
  Purchase #6 $100.69   13.347%   $114.1291   $114.13   $114.15   $114.10  
  Purchase #7 $34.28   5.202%   $36.0632   $36.06   $36.05   $36.10  
  7 purchase totals = $923.43       $989.8919   $989.88   $989.90   $989.90