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 $183.52   12.839%   $207.0821   $207.08   $207.10   $207.10  
  Purchase #2 $207.49   9.351%   $226.8924   $226.89   $226.90   $226.90  
  Purchase #3 $161.44   7.763%   $173.9726   $173.97   $173.95   $174.00  
  Purchase #4 $216.61   10.311%   $238.9447   $238.94   $238.95   $238.90  
  Purchase #5 $113.65   5.587%   $119.9996   $120.00   $120.00   $120.00  
  Purchase #6 $183.58   13.832%   $208.9728   $208.97   $208.95   $209.00  
  Purchase #7 $59.75   10.509%   $66.0291   $66.03   $66.05   $66.00  
  7 purchase totals = $1,126.04       $1,241.8933   $1,241.88   $1,241.90   $1,241.90