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 $60.57   13.370%   $68.6682   $68.67   $68.65   $68.70  
  Purchase #2 $193.94   8.535%   $210.4928   $210.49   $210.50   $210.50  
  Purchase #3 $214.47   10.828%   $237.6928   $237.69   $237.70   $237.70  
  Purchase #4 $242.92   6.656%   $259.0888   $259.09   $259.10   $259.10  
  Purchase #5 $113.93   5.411%   $120.0948   $120.09   $120.10   $120.10  
  Purchase #6 $61.26   11.631%   $68.3852   $68.39   $68.40   $68.40  
  Purchase #7 $209.62   6.801%   $223.8763   $223.88   $223.90   $223.90  
  7 purchase totals = $1,096.71       $1,188.2989   $1,188.30   $1,188.35   $1,188.40