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 $165.88   4.734%   $173.7328   $173.73   $173.75   $173.70  
  Purchase #2 $186.95   13.115%   $211.4685   $211.47   $211.45   $211.50  
  Purchase #3 $202.81   4.818%   $212.5814   $212.58   $212.60   $212.60  
  Purchase #4 $68.65   12.350%   $77.1283   $77.13   $77.15   $77.10  
  Purchase #5 $129.44   9.182%   $141.3252   $141.33   $141.35   $141.30  
  Purchase #6 $176.38   5.301%   $185.7299   $185.73   $185.75   $185.70  
  Purchase #7 $239.26   11.783%   $267.452   $267.45   $267.45   $267.50  
  7 purchase totals = $1,169.37       $1,269.4181   $1,269.42   $1,269.50   $1,269.40