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 $179.59   8.380%   $194.6396   $194.64   $194.65   $194.60  
  Purchase #2 $236.56   12.661%   $266.5109   $266.51   $266.50   $266.50  
  Purchase #3 $38.26   5.509%   $40.3677   $40.37   $40.35   $40.40  
  Purchase #4 $154.98   11.680%   $173.0817   $173.08   $173.10   $173.10  
  Purchase #5 $239.94   9.567%   $262.8951   $262.90   $262.90   $262.90  
  Purchase #6 $41.80   6.500%   $44.517   $44.52   $44.50   $44.50  
  Purchase #7 $111.28   12.791%   $125.5138   $125.51   $125.50   $125.50  
  7 purchase totals = $1,002.41       $1,107.5258   $1,107.53   $1,107.50   $1,107.50