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 $142.97   5.560%   $150.9191   $150.92   $150.90   $150.90  
  Purchase #2 $137.75   11.858%   $154.0844   $154.08   $154.10   $154.10  
  Purchase #3 $109.60   5.407%   $115.5261   $115.53   $115.55   $115.50  
  Purchase #4 $224.26   13.136%   $253.7188   $253.72   $253.70   $253.70  
  Purchase #5 $161.43   6.551%   $172.0053   $172.01   $172.00   $172.00  
  Purchase #6 $209.41   10.762%   $231.9467   $231.95   $231.95   $231.90  
  Purchase #7 $51.91   6.397%   $55.2307   $55.23   $55.25   $55.20  
  7 purchase totals = $1,037.33       $1,133.4311   $1,133.44   $1,133.45   $1,133.30