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 $183.48   4.780%   $192.2503   $192.25   $192.25   $192.30  
  Purchase #2 $58.60   11.175%   $65.1486   $65.15   $65.15   $65.10  
  Purchase #3 $92.50   13.310%   $104.8118   $104.81   $104.80   $104.80  
  Purchase #4 $169.60   3.781%   $176.0126   $176.01   $176.00   $176.00  
  Purchase #5 $93.81   13.636%   $106.6019   $106.60   $106.60   $106.60  
  Purchase #6 $24.80   10.830%   $27.4858   $27.49   $27.50   $27.50  
  Purchase #7 $192.80   6.861%   $206.028   $206.03   $206.05   $206.00  
  7 purchase totals = $815.59       $878.3390   $878.34   $878.35   $878.30