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 $109.73   3.218%   $113.2611   $113.26   $113.25   $113.30  
  Purchase #2 $99.85   6.462%   $106.3023   $106.30   $106.30   $106.30  
  Purchase #3 $246.70   8.168%   $266.8505   $266.85   $266.85   $266.90  
  Purchase #4 $153.71   4.153%   $160.0936   $160.09   $160.10   $160.10  
  Purchase #5 $27.60   9.168%   $30.1304   $30.13   $30.15   $30.10  
  Purchase #6 $176.57   10.434%   $194.9933   $194.99   $195.00   $195.00  
  Purchase #7 $84.50   8.759%   $91.9014   $91.90   $91.90   $91.90  
  7 purchase totals = $898.66       $963.5326   $963.52   $963.55   $963.60