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	$34.70	7.639%	$37.3507	$37.35	$37.35	$37.40
Purchase #2	$112.86	5.355%	$118.9037	$118.90	$118.90	$118.90
Purchase #3	$87.30	8.706%	$94.9003	$94.90	$94.90	$94.90
Purchase #4	$217.58	4.472%	$227.3102	$227.31	$227.30	$227.30
Purchase #5	$41.65	4.759%	$43.6321	$43.63	$43.65	$43.60
Purchase #6	$91.36	5.506%	$96.3903	$96.39	$96.40	$96.40
Purchase #7	$143.86	5.511%	$151.7881	$151.79	$151.80	$151.80
7 purchase totals =	$729.31		$770.2754	$770.27	$770.30	$770.30