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	$102.60	8.708%	$111.5344	$111.53	$111.55	$111.50
Purchase #2	$71.30	11.511%	$79.5073	$79.51	$79.50	$79.50
Purchase #3	$176.62	12.477%	$198.6569	$198.66	$198.65	$198.70
Purchase #4	$110.91	6.826%	$118.4807	$118.48	$118.50	$118.50
Purchase #5	$127.89	5.280%	$134.6426	$134.64	$134.65	$134.60
Purchase #6	$103.56	6.418%	$110.2065	$110.21	$110.20	$110.20
Purchase #7	$72.49	13.432%	$82.2269	$82.23	$82.25	$82.20
7 purchase totals =	$765.37		$835.2553	$835.26	$835.30	$835.20