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 $210.67   6.206%   $223.7442   $223.74   $223.75   $223.70  
  Purchase #2 $70.42   4.291%   $73.4417   $73.44   $73.45   $73.40  
  Purchase #3 $97.68   4.683%   $102.2544   $102.25   $102.25   $102.30  
  Purchase #4 $121.48   4.682%   $127.1677   $127.17   $127.15   $127.20  
  Purchase #5 $159.58   12.642%   $179.7541   $179.75   $179.75   $179.80  
  Purchase #6 $208.91   8.446%   $226.5545   $226.55   $226.55   $226.60  
  Purchase #7 $192.67   3.132%   $198.7044   $198.70   $198.70   $198.70  
  7 purchase totals = $1,061.41       $1,131.6210   $1,131.60   $1,131.60   $1,131.70