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	$109.74	12.424%	$123.3741	$123.37	$123.35	$123.40
Purchase #2	$46.63	3.504%	$48.2639	$48.26	$48.25	$48.30
Purchase #3	$248.58	8.726%	$270.2711	$270.27	$270.25	$270.30
Purchase #4	$33.27	11.601%	$37.1297	$37.13	$37.15	$37.10
Purchase #5	$118.74	11.106%	$131.9273	$131.93	$131.95	$131.90
Purchase #6	$209.59	7.311%	$224.9131	$224.91	$224.90	$224.90
Purchase #7	$217.86	4.798%	$228.3129	$228.31	$228.30	$228.30
7 purchase totals =	$984.41		$1,064.1921	$1,064.18	$1,064.15	$1,064.20