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	$209.78	13.608%	$238.3269	$238.33	$238.35	$238.30
Purchase #2	$224.94	7.288%	$241.3336	$241.33	$241.35	$241.30
Purchase #3	$152.36	12.739%	$171.7691	$171.77	$171.75	$171.80
Purchase #4	$70.78	11.242%	$78.7371	$78.74	$78.75	$78.70
Purchase #5	$29.59	4.159%	$30.8206	$30.82	$30.80	$30.80
Purchase #6	$203.69	3.829%	$211.4893	$211.49	$211.50	$211.50
Purchase #7	$159.47	9.497%	$174.6149	$174.61	$174.60	$174.60
7 purchase totals =	$1,050.61		$1,147.0915	$1,147.09	$1,147.10	$1,147.00