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 $164.65   13.261%   $186.4842   $186.48   $186.50   $186.50  
  Purchase #2 $226.56   6.529%   $241.3521   $241.35   $241.35   $241.40  
  Purchase #3 $182.42   5.655%   $192.7359   $192.74   $192.75   $192.70  
  Purchase #4 $87.40   10.581%   $96.6478   $96.65   $96.65   $96.60  
  Purchase #5 $134.60   3.459%   $139.2558   $139.26   $139.25   $139.30  
  Purchase #6 $227.88   9.246%   $248.9498   $248.95   $248.95   $248.90  
  Purchase #7 $189.31   6.571%   $201.7496   $201.75   $201.75   $201.70  
  7 purchase totals = $1,212.82       $1,307.1752   $1,307.18   $1,307.20   $1,307.10