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 $234.54   11.728%   $262.0469   $262.05   $262.05   $262.00  
  Purchase #2 $172.51   8.184%   $186.6282   $186.63   $186.65   $186.60  
  Purchase #3 $48.37   11.659%   $54.0095   $54.01   $54.00   $54.00  
  Purchase #4 $165.94   4.729%   $173.7873   $173.79   $173.80   $173.80  
  Purchase #5 $13.41   13.206%   $15.1809   $15.18   $15.20   $15.20  
  Purchase #6 $73.75   12.296%   $82.8183   $82.82   $82.80   $82.80  
  Purchase #7 $211.72   4.585%   $221.4274   $221.43   $221.45   $221.40  
  7 purchase totals = $920.24       $995.8985   $995.91   $995.95   $995.80