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 $135.59   11.820%   $151.6167   $151.62   $151.60   $151.60  
  Purchase #2 $13.94   10.204%   $15.3624   $15.36   $15.35   $15.40  
  Purchase #3 $66.63   3.700%   $69.0953   $69.10   $69.10   $69.10  
  Purchase #4 $183.55   3.153%   $189.3373   $189.34   $189.35   $189.30  
  Purchase #5 $53.33   6.140%   $56.6045   $56.60   $56.60   $56.60  
  Purchase #6 $10.51   10.434%   $11.6066   $11.61   $11.60   $11.60  
  Purchase #7 $193.57   9.151%   $211.2836   $211.28   $211.30   $211.30  
  7 purchase totals = $657.12       $704.9064   $704.91   $704.90   $704.90