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	$234.60	12.665%	$264.3121	$264.31	$264.30	$264.30
Purchase #2	$166.42	5.251%	$175.1587	$175.16	$175.15	$175.20
Purchase #3	$146.29	6.285%	$155.4843	$155.48	$155.50	$155.50
Purchase #4	$166.25	13.317%	$188.3895	$188.39	$188.40	$188.40
Purchase #5	$206.32	4.847%	$216.3203	$216.32	$216.30	$216.30
Purchase #6	$250.97	7.131%	$268.8667	$268.87	$268.85	$268.90
Purchase #7	$52.72	9.591%	$57.7764	$57.78	$57.80	$57.80
7 purchase totals =	$1,223.57		$1,326.3080	$1,326.31	$1,326.30	$1,326.40