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 $245.50   13.486%   $278.6081   $278.61   $278.60   $278.60  
  Purchase #2 $232.88   9.260%   $254.4447   $254.44   $254.45   $254.40  
  Purchase #3 $62.43   7.734%   $67.2583   $67.26   $67.25   $67.30  
  Purchase #4 $191.58   4.702%   $200.5881   $200.59   $200.60   $200.60  
  Purchase #5 $226.85   9.537%   $248.4847   $248.48   $248.50   $248.50  
  Purchase #6 $145.91   4.582%   $152.5956   $152.60   $152.60   $152.60  
  Purchase #7 $58.74   7.835%   $63.3423   $63.34   $63.35   $63.30  
  7 purchase totals = $1,163.89       $1,265.3218   $1,265.32   $1,265.35   $1,265.30