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	$136.40	3.829%	$141.6228	$141.62	$141.60	$141.60
Purchase #2	$216.25	12.371%	$243.0023	$243.00	$243.00	$243.00
Purchase #3	$123.44	8.803%	$134.3064	$134.31	$134.30	$134.30
Purchase #4	$61.62	10.113%	$67.8516	$67.85	$67.85	$67.90
Purchase #5	$31.94	11.635%	$35.6562	$35.66	$35.65	$35.70
Purchase #6	$162.71	7.815%	$175.4258	$175.43	$175.45	$175.40
Purchase #7	$168.28	7.503%	$180.906	$180.91	$180.90	$180.90
7 purchase totals =	$900.64		$978.7711	$978.78	$978.75	$978.80