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	$79.78	3.710%	$82.7398	$82.74	$82.75	$82.70
Purchase #2	$145.78	8.746%	$158.5299	$158.53	$158.55	$158.50
Purchase #3	$201.91	6.361%	$214.7535	$214.75	$214.75	$214.80
Purchase #4	$220.60	13.765%	$250.9656	$250.97	$250.95	$251.00
Purchase #5	$80.32	11.702%	$89.719	$89.72	$89.70	$89.70
Purchase #6	$110.74	11.833%	$123.8439	$123.84	$123.85	$123.80
Purchase #7	$166.47	9.834%	$182.8407	$182.84	$182.85	$182.80
7 purchase totals =	$1,005.60		$1,103.3924	$1,103.39	$1,103.40	$1,103.30