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 $84.68   9.474%   $92.7026   $92.70   $92.70   $92.70  
  Purchase #2 $55.45   11.432%   $61.789   $61.79   $61.80   $61.80  
  Purchase #3 $163.58   11.589%   $182.5373   $182.54   $182.55   $182.50  
  Purchase #4 $91.36   8.538%   $99.1603   $99.16   $99.15   $99.20  
  Purchase #5 $118.87   12.207%   $133.3805   $133.38   $133.40   $133.40  
  Purchase #6 $164.38   5.732%   $173.8023   $173.80   $173.80   $173.80  
  Purchase #7 $177.60   12.167%   $199.2086   $199.21   $199.20   $199.20  
  7 purchase totals = $855.92       $942.5806   $942.58   $942.60   $942.60