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	$114.78	11.644%	$128.145	$128.15	$128.15	$128.10
Purchase #2	$115.90	6.391%	$123.3072	$123.31	$123.30	$123.30
Purchase #3	$124.51	5.567%	$131.4415	$131.44	$131.45	$131.40
Purchase #4	$95.49	3.313%	$98.6536	$98.65	$98.65	$98.70
Purchase #5	$53.51	4.512%	$55.9244	$55.92	$55.90	$55.90
Purchase #6	$65.58	4.515%	$68.5409	$68.54	$68.55	$68.50
Purchase #7	$47.59	5.558%	$50.2351	$50.24	$50.25	$50.20
7 purchase totals =	$617.36		$656.2477	$656.25	$656.25	$656.10