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	$110.60	11.653%	$123.4882	$123.49	$123.50	$123.50
Purchase #2	$88.85	3.271%	$91.7563	$91.76	$91.75	$91.80
Purchase #3	$105.33	9.543%	$115.3816	$115.38	$115.40	$115.40
Purchase #4	$38.50	5.158%	$40.4858	$40.49	$40.50	$40.50
Purchase #5	$170.79	12.173%	$191.5803	$191.58	$191.60	$191.60
Purchase #6	$95.46	4.760%	$100.0039	$100.00	$100.00	$100.00
Purchase #7	$139.59	11.304%	$155.3693	$155.37	$155.35	$155.40
7 purchase totals =	$749.12		$818.0654	$818.07	$818.10	$818.20