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 $84.87   12.246%   $95.2632   $95.26   $95.25   $95.30  
  Purchase #2 $77.30   4.701%   $80.9339   $80.93   $80.95   $80.90  
  Purchase #3 $108.87   13.597%   $123.6731   $123.67   $123.65   $123.70  
  Purchase #4 $223.68   8.779%   $243.3169   $243.32   $243.30   $243.30  
  Purchase #5 $221.30   5.269%   $232.9603   $232.96   $232.95   $233.00  
  Purchase #6 $228.92   4.476%   $239.1665   $239.17   $239.15   $239.20  
  Purchase #7 $71.75   7.408%   $77.0652   $77.07   $77.05   $77.10  
  7 purchase totals = $1,016.69       $1,092.3791   $1,092.38   $1,092.30   $1,092.50