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 $69.37   9.789%   $76.1606   $76.16   $76.15   $76.20  
  Purchase #2 $105.59   4.426%   $110.2634   $110.26   $110.25   $110.30  
  Purchase #3 $218.35   9.127%   $238.2788   $238.28   $238.30   $238.30  
  Purchase #4 $54.49   3.835%   $56.5797   $56.58   $56.60   $56.60  
  Purchase #5 $38.44   5.817%   $40.6761   $40.68   $40.70   $40.70  
  Purchase #6 $122.87   10.501%   $135.7726   $135.77   $135.75   $135.80  
  Purchase #7 $186.72   6.569%   $198.9856   $198.99   $199.00   $199.00  
  7 purchase totals = $795.83       $856.7168   $856.72   $856.75   $856.90