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 $63.79   8.403%   $69.1503   $69.15   $69.15   $69.20  
  Purchase #2 $106.70   7.311%   $114.5008   $114.50   $114.50   $114.50  
  Purchase #3 $175.60   12.818%   $198.1084   $198.11   $198.10   $198.10  
  Purchase #4 $80.71   8.533%   $87.597   $87.60   $87.60   $87.60  
  Purchase #5 $162.72   12.561%   $183.1593   $183.16   $183.15   $183.20  
  Purchase #6 $90.52   6.392%   $96.306   $96.31   $96.30   $96.30  
  Purchase #7 $20.91   8.699%   $22.729   $22.73   $22.75   $22.70  
  7 purchase totals = $700.95       $771.5508   $771.56   $771.55   $771.60