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 $66.98   3.760%   $69.4984   $69.50   $69.50   $69.50  
  Purchase #2 $109.87   3.556%   $113.777   $113.78   $113.80   $113.80  
  Purchase #3 $207.96   8.157%   $224.9233   $224.92   $224.90   $224.90  
  Purchase #4 $104.49   13.521%   $118.6181   $118.62   $118.60   $118.60  
  Purchase #5 $50.55   11.622%   $56.4249   $56.42   $56.40   $56.40  
  Purchase #6 $52.30   3.145%   $53.9448   $53.94   $53.95   $53.90  
  Purchase #7 $247.88   7.814%   $267.2493   $267.25   $267.25   $267.20  
  7 purchase totals = $840.03       $904.4358   $904.43   $904.40   $904.30