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 $163.53   13.769%   $186.0464   $186.05   $186.05   $186.00  
  Purchase #2 $68.98   3.571%   $71.4433   $71.44   $71.45   $71.40  
  Purchase #3 $211.35   6.836%   $225.7979   $225.80   $225.80   $225.80  
  Purchase #4 $155.81   13.330%   $176.5795   $176.58   $176.60   $176.60  
  Purchase #5 $35.51   8.359%   $38.4783   $38.48   $38.50   $38.50  
  Purchase #6 $190.50   8.166%   $206.0562   $206.06   $206.05   $206.10  
  Purchase #7 $22.69   11.663%   $25.3363   $25.34   $25.35   $25.30  
  7 purchase totals = $848.37       $929.7379   $929.75   $929.80   $929.70