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 $180.72   8.139%   $195.4288   $195.43   $195.45   $195.40  
  Purchase #2 $113.91   3.271%   $117.636   $117.64   $117.65   $117.60  
  Purchase #3 $126.82   10.869%   $140.6041   $140.60   $140.60   $140.60  
  Purchase #4 $169.53   13.413%   $192.2691   $192.27   $192.25   $192.30  
  Purchase #5 $90.65   8.874%   $98.6943   $98.69   $98.70   $98.70  
  Purchase #6 $28.49   7.368%   $30.5891   $30.59   $30.60   $30.60  
  Purchase #7 $230.49   13.829%   $262.3645   $262.36   $262.35   $262.40  
  7 purchase totals = $940.61       $1,037.5859   $1,037.58   $1,037.60   $1,037.60