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 $107.83   13.397%   $122.276   $122.28   $122.30   $122.30  
  Purchase #2 $58.56   8.440%   $63.5025   $63.50   $63.50   $63.50  
  Purchase #3 $55.49   13.675%   $63.0783   $63.08   $63.10   $63.10  
  Purchase #4 $162.89   5.739%   $172.2383   $172.24   $172.25   $172.20  
  Purchase #5 $186.38   4.146%   $194.1073   $194.11   $194.10   $194.10  
  Purchase #6 $104.82   11.835%   $117.2254   $117.23   $117.25   $117.20  
  Purchase #7 $232.28   11.475%   $258.9341   $258.93   $258.95   $258.90  
  7 purchase totals = $908.25       $991.3619   $991.37   $991.45   $991.30