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 $232.72   6.604%   $248.0888   $248.09   $248.10   $248.10  
  Purchase #2 $150.94   11.688%   $168.5819   $168.58   $168.60   $168.60  
  Purchase #3 $57.84   5.449%   $60.9917   $60.99   $61.00   $61.00  
  Purchase #4 $244.43   7.393%   $262.5007   $262.50   $262.50   $262.50  
  Purchase #5 $115.39   3.232%   $119.1194   $119.12   $119.10   $119.10  
  Purchase #6 $182.91   13.448%   $207.5077   $207.51   $207.50   $207.50  
  Purchase #7 $159.75   5.214%   $168.0794   $168.08   $168.10   $168.10  
  7 purchase totals = $1,143.98       $1,234.8696   $1,234.87   $1,234.90   $1,234.90