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 $241.78   8.292%   $261.8284   $261.83   $261.85   $261.80  
  Purchase #2 $202.30   4.603%   $211.6119   $211.61   $211.60   $211.60  
  Purchase #3 $98.51   10.357%   $108.7127   $108.71   $108.70   $108.70  
  Purchase #4 $192.83   11.278%   $214.5774   $214.58   $214.60   $214.60  
  Purchase #5 $161.33   13.678%   $183.3967   $183.40   $183.40   $183.40  
  Purchase #6 $61.94   11.365%   $68.9795   $68.98   $69.00   $69.00  
  Purchase #7 $141.59   13.771%   $161.0884   $161.09   $161.10   $161.10  
  7 purchase totals = $1,100.28       $1,210.1950   $1,210.20   $1,210.25   $1,210.20