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 $87.97   10.250%   $96.9869   $96.99   $97.00   $97.00  
  Purchase #2 $208.50   11.250%   $231.9563   $231.96   $231.95   $232.00  
  Purchase #3 $170.95   12.710%   $192.6777   $192.68   $192.70   $192.70  
  Purchase #4 $190.73   9.517%   $208.8818   $208.88   $208.90   $208.90  
  Purchase #5 $201.93   3.238%   $208.4685   $208.47   $208.45   $208.50  
  Purchase #6 $73.74   11.110%   $81.9325   $81.93   $81.95   $81.90  
  Purchase #7 $105.33   9.734%   $115.5828   $115.58   $115.60   $115.60  
  7 purchase totals = $1,039.15       $1,136.4865   $1,136.49   $1,136.55   $1,136.60