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	$37.65	6.468%	$40.0852	$40.09	$40.10	$40.10
Purchase #2	$215.60	12.364%	$242.2568	$242.26	$242.25	$242.30
Purchase #3	$25.96	11.472%	$28.9381	$28.94	$28.95	$28.90
Purchase #4	$108.32	4.289%	$112.9658	$112.97	$112.95	$113.00
Purchase #5	$64.67	13.238%	$73.231	$73.23	$73.25	$73.20
Purchase #6	$31.65	6.369%	$33.6658	$33.67	$33.65	$33.70
Purchase #7	$109.63	12.336%	$123.154	$123.15	$123.15	$123.20
7 purchase totals =	$593.48		$654.2967	$654.31	$654.30	$654.40