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 $96.47   4.744%   $101.0465   $101.05   $101.05   $101.00  
  Purchase #2 $103.65   3.669%   $107.4529   $107.45   $107.45   $107.50  
  Purchase #3 $242.80   4.167%   $252.9175   $252.92   $252.90   $252.90  
  Purchase #4 $152.44   6.120%   $161.7693   $161.77   $161.75   $161.80  
  Purchase #5 $155.31   4.129%   $161.7227   $161.72   $161.70   $161.70  
  Purchase #6 $127.63   10.873%   $141.5072   $141.51   $141.50   $141.50  
  Purchase #7 $141.88   11.463%   $158.1437   $158.14   $158.15   $158.10  
  7 purchase totals = $1,020.18       $1,084.5598   $1,084.56   $1,084.50   $1,084.50