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	$142.28	12.719%	$160.3766	$160.38	$160.40	$160.40
Purchase #2	$6.83	6.579%	$7.2793	$7.28	$7.30	$7.30
Purchase #3	$33.57	8.218%	$36.3288	$36.33	$36.35	$36.30
Purchase #4	$123.66	4.129%	$128.7659	$128.77	$128.75	$128.80
Purchase #5	$46.36	12.842%	$52.3136	$52.31	$52.30	$52.30
Purchase #6	$45.65	5.472%	$48.148	$48.15	$48.15	$48.10
Purchase #7	$200.59	3.812%	$208.2365	$208.24	$208.25	$208.20
7 purchase totals =	$598.94		$641.4487	$641.46	$641.50	$641.40