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 $241.33   11.528%   $269.1505   $269.15   $269.15   $269.20  
  Purchase #2 $28.33   3.567%   $29.3405   $29.34   $29.35   $29.30  
  Purchase #3 $60.82   6.755%   $64.9284   $64.93   $64.95   $64.90  
  Purchase #4 $42.77   9.670%   $46.9059   $46.91   $46.90   $46.90  
  Purchase #5 $64.25   9.257%   $70.1976   $70.20   $70.20   $70.20  
  Purchase #6 $97.52   3.267%   $100.706   $100.71   $100.70   $100.70  
  Purchase #7 $248.90   11.522%   $277.5783   $277.58   $277.60   $277.60  
  7 purchase totals = $783.92       $858.8072   $858.82   $858.85   $858.80