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	$248.56	8.187%	$268.9096	$268.91	$268.90	$268.90
Purchase #2	$129.30	10.297%	$142.614	$142.61	$142.60	$142.60
Purchase #3	$180.41	3.697%	$187.0798	$187.08	$187.10	$187.10
Purchase #4	$173.83	7.639%	$187.1089	$187.11	$187.10	$187.10
Purchase #5	$222.91	5.696%	$235.607	$235.61	$235.60	$235.60
Purchase #6	$38.75	4.621%	$40.5406	$40.54	$40.55	$40.50
Purchase #7	$190.59	13.741%	$216.779	$216.78	$216.80	$216.80
7 purchase totals =	$1,184.35		$1,278.6389	$1,278.64	$1,278.65	$1,278.60