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 $50.55   12.130%   $56.6817   $56.68   $56.70   $56.70  
  Purchase #2 $238.78   13.308%   $270.5568   $270.56   $270.55   $270.60  
  Purchase #3 $153.95   12.702%   $173.5047   $173.50   $173.50   $173.50  
  Purchase #4 $82.33   5.386%   $86.7643   $86.76   $86.75   $86.80  
  Purchase #5 $215.51   10.387%   $237.895   $237.90   $237.90   $237.90  
  Purchase #6 $187.59   12.521%   $211.0781   $211.08   $211.10   $211.10  
  Purchase #7 $90.63   3.754%   $94.0323   $94.03   $94.05   $94.00  
  7 purchase totals = $1,019.34       $1,130.5129   $1,130.51   $1,130.55   $1,130.60