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 $219.69   10.706%   $243.21   $243.21   $243.20   $243.20  
  Purchase #2 $186.74   6.324%   $198.5494   $198.55   $198.55   $198.50  
  Purchase #3 $61.43   11.435%   $68.4545   $68.45   $68.45   $68.50  
  Purchase #4 $185.48   10.565%   $205.076   $205.08   $205.10   $205.10  
  Purchase #5 $155.99   13.640%   $177.267   $177.27   $177.25   $177.30  
  Purchase #6 $233.40   13.861%   $265.7516   $265.75   $265.75   $265.80  
  Purchase #7 $94.33   7.365%   $101.2774   $101.28   $101.30   $101.30  
  7 purchase totals = $1,137.06       $1,259.5859   $1,259.59   $1,259.60   $1,259.70