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 $59.54   3.368%   $61.5453   $61.55   $61.55   $61.50  
  Purchase #2 $46.78   10.251%   $51.5754   $51.58   $51.60   $51.60  
  Purchase #3 $219.55   8.679%   $238.6047   $238.60   $238.60   $238.60  
  Purchase #4 $98.65   9.383%   $107.9063   $107.91   $107.90   $107.90  
  Purchase #5 $178.84   9.410%   $195.6688   $195.67   $195.65   $195.70  
  Purchase #6 $94.27   10.534%   $104.2004   $104.20   $104.20   $104.20  
  Purchase #7 $226.59   5.622%   $239.3289   $239.33   $239.35   $239.30  
  7 purchase totals = $924.22       $998.8298   $998.84   $998.85   $998.80