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 $173.81   12.719%   $195.9169   $195.92   $195.90   $195.90  
  Purchase #2 $144.63   10.327%   $159.5659   $159.57   $159.55   $159.60  
  Purchase #3 $94.53   3.730%   $98.056   $98.06   $98.05   $98.10  
  Purchase #4 $146.78   8.364%   $159.0567   $159.06   $159.05   $159.10  
  Purchase #5 $147.40   11.550%   $164.4247   $164.42   $164.40   $164.40  
  Purchase #6 $196.40   13.273%   $222.4682   $222.47   $222.45   $222.50  
  Purchase #7 $241.31   9.283%   $263.7108   $263.71   $263.70   $263.70  
  7 purchase totals = $1,144.86       $1,263.1992   $1,263.21   $1,263.10   $1,263.30