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 $49.49   8.278%   $53.5868   $53.59   $53.60   $53.60  
  Purchase #2 $113.66   6.624%   $121.1888   $121.19   $121.20   $121.20  
  Purchase #3 $226.49   13.773%   $257.6845   $257.68   $257.70   $257.70  
  Purchase #4 $154.33   8.179%   $166.9527   $166.95   $166.95   $167.00  
  Purchase #5 $88.49   7.442%   $95.0754   $95.08   $95.10   $95.10  
  Purchase #6 $151.36   6.671%   $161.4572   $161.46   $161.45   $161.50  
  Purchase #7 $229.34   7.217%   $245.8915   $245.89   $245.90   $245.90  
  7 purchase totals = $1,013.16       $1,101.8369   $1,101.84   $1,101.90   $1,102.00