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 $35.77   7.254%   $38.3648   $38.36   $38.35   $38.40  
  Purchase #2 $250.97   6.197%   $266.5226   $266.52   $266.50   $266.50  
  Purchase #3 $75.66   8.716%   $82.2545   $82.25   $82.25   $82.30  
  Purchase #4 $24.63   9.872%   $27.0615   $27.06   $27.05   $27.10  
  Purchase #5 $69.26   6.409%   $73.6989   $73.70   $73.70   $73.70  
  Purchase #6 $248.59   13.303%   $281.6599   $281.66   $281.65   $281.70  
  Purchase #7 $74.92   7.559%   $80.5832   $80.58   $80.60   $80.60  
  7 purchase totals = $779.80       $850.1454   $850.13   $850.10   $850.30