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 $194.71   8.169%   $210.6159   $210.62   $210.60   $210.60  
  Purchase #2 $218.70   12.114%   $245.1933   $245.19   $245.20   $245.20  
  Purchase #3 $137.99   9.423%   $150.9928   $150.99   $151.00   $151.00  
  Purchase #4 $207.83   13.555%   $236.0014   $236.00   $236.00   $236.00  
  Purchase #5 $83.76   13.728%   $95.2586   $95.26   $95.25   $95.30  
  Purchase #6 $56.94   13.411%   $64.5762   $64.58   $64.60   $64.60  
  Purchase #7 $163.28   6.743%   $174.29   $174.29   $174.30   $174.30  
  7 purchase totals = $1,063.21       $1,176.9282   $1,176.93   $1,176.95   $1,177.00