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	$29.82	9.318%	$32.5986	$32.60	$32.60	$32.60
Purchase #2	$32.88	7.829%	$35.4542	$35.45	$35.45	$35.50
Purchase #3	$134.73	7.741%	$145.1594	$145.16	$145.15	$145.20
Purchase #4	$201.51	4.554%	$210.6868	$210.69	$210.70	$210.70
Purchase #5	$166.81	12.112%	$187.014	$187.01	$187.00	$187.00
Purchase #6	$112.34	9.760%	$123.3044	$123.30	$123.30	$123.30
Purchase #7	$79.79	12.148%	$89.4829	$89.48	$89.50	$89.50
7 purchase totals =	$757.88		$823.7003	$823.69	$823.70	$823.80