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 $176.45   8.273%   $191.0477   $191.05   $191.05   $191.00  
  Purchase #2 $141.94   11.194%   $157.8288   $157.83   $157.85   $157.80  
  Purchase #3 $85.90   8.268%   $93.0022   $93.00   $93.00   $93.00  
  Purchase #4 $222.38   4.504%   $232.396   $232.40   $232.40   $232.40  
  Purchase #5 $79.53   13.495%   $90.2626   $90.26   $90.25   $90.30  
  Purchase #6 $62.93   4.516%   $65.7719   $65.77   $65.75   $65.80  
  Purchase #7 $233.80   8.197%   $252.9646   $252.96   $252.95   $253.00  
  7 purchase totals = $1,002.93       $1,083.2738   $1,083.27   $1,083.25   $1,083.30