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	$249.32	8.631%	$270.8388	$270.84	$270.85	$270.80
Purchase #2	$222.52	6.158%	$236.2228	$236.22	$236.20	$236.20
Purchase #3	$208.26	10.181%	$229.463	$229.46	$229.45	$229.50
Purchase #4	$211.47	11.673%	$236.1549	$236.15	$236.15	$236.20
Purchase #5	$39.40	10.128%	$43.3904	$43.39	$43.40	$43.40
Purchase #6	$181.46	8.139%	$196.229	$196.23	$196.25	$196.20
Purchase #7	$28.33	11.601%	$31.6166	$31.62	$31.60	$31.60
7 purchase totals =	$1,140.76		$1,243.9155	$1,243.91	$1,243.90	$1,243.90