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   8.546%   $53.7194   $53.72   $53.70   $53.70  
  Purchase #2 $213.71   7.549%   $229.843   $229.84   $229.85   $229.80  
  Purchase #3 $233.43   10.771%   $258.5727   $258.57   $258.55   $258.60  
  Purchase #4 $224.81   7.278%   $241.1717   $241.17   $241.15   $241.20  
  Purchase #5 $208.42   3.125%   $214.9331   $214.93   $214.95   $214.90  
  Purchase #6 $92.40   13.870%   $105.2159   $105.22   $105.20   $105.20  
  Purchase #7 $156.26   3.357%   $161.5056   $161.51   $161.50   $161.50  
  7 purchase totals = $1,178.52       $1,264.9614   $1,264.96   $1,264.90   $1,264.90