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 $50.39   6.172%   $53.5001   $53.50   $53.50   $53.50  
  Purchase #2 $201.35   6.871%   $215.1848   $215.18   $215.20   $215.20  
  Purchase #3 $166.96   7.344%   $179.2215   $179.22   $179.20   $179.20  
  Purchase #4 $240.69   7.552%   $258.8669   $258.87   $258.85   $258.90  
  Purchase #5 $57.99   5.448%   $61.1493   $61.15   $61.15   $61.10  
  Purchase #6 $129.55   4.679%   $135.6116   $135.61   $135.60   $135.60  
  Purchase #7 $101.27   9.147%   $110.5332   $110.53   $110.55   $110.50  
  7 purchase totals = $948.20       $1,014.0674   $1,014.06   $1,014.05   $1,014.00