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 $89.52   6.561%   $95.3934   $95.39   $95.40   $95.40  
  Purchase #2 $150.94   9.442%   $165.1918   $165.19   $165.20   $165.20  
  Purchase #3 $185.66   4.429%   $193.8829   $193.88   $193.90   $193.90  
  Purchase #4 $150.79   3.567%   $156.1687   $156.17   $156.15   $156.20  
  Purchase #5 $106.38   7.212%   $114.0521   $114.05   $114.05   $114.10  
  Purchase #6 $248.63   11.407%   $276.9912   $276.99   $277.00   $277.00  
  Purchase #7 $148.46   11.437%   $165.4394   $165.44   $165.45   $165.40  
  7 purchase totals = $1,080.38       $1,167.1195   $1,167.11   $1,167.15   $1,167.20