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 $72.29   12.246%   $81.1426   $81.14   $81.15   $81.10  
  Purchase #2 $146.42   3.578%   $151.6589   $151.66   $151.65   $151.70  
  Purchase #3 $163.32   9.601%   $179.0004   $179.00   $179.00   $179.00  
  Purchase #4 $119.36   6.833%   $127.5159   $127.52   $127.50   $127.50  
  Purchase #5 $118.91   10.157%   $130.9877   $130.99   $131.00   $131.00  
  Purchase #6 $200.76   12.864%   $226.5858   $226.59   $226.60   $226.60  
  Purchase #7 $80.38   4.194%   $83.7511   $83.75   $83.75   $83.80  
  7 purchase totals = $901.44       $980.6424   $980.65   $980.65   $980.70