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 $84.60   7.581%   $91.0135   $91.01   $91.00   $91.00  
  Purchase #2 $229.39   10.493%   $253.4599   $253.46   $253.45   $253.50  
  Purchase #3 $85.30   12.597%   $96.0452   $96.05   $96.05   $96.00  
  Purchase #4 $205.48   11.423%   $228.952   $228.95   $228.95   $229.00  
  Purchase #5 $109.48   4.453%   $114.3551   $114.36   $114.35   $114.40  
  Purchase #6 $242.89   11.458%   $270.7203   $270.72   $270.70   $270.70  
  Purchase #7 $250.26   12.712%   $282.0731   $282.07   $282.05   $282.10  
  7 purchase totals = $1,207.40       $1,336.6191   $1,336.62   $1,336.55   $1,336.70