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	$165.94	3.215%	$171.275	$171.28	$171.30	$171.30
Purchase #2	$5.83	13.858%	$6.6379	$6.64	$6.65	$6.60
Purchase #3	$56.27	11.432%	$62.7028	$62.70	$62.70	$62.70
Purchase #4	$7.64	4.657%	$7.9958	$8.00	$8.00	$8.00
Purchase #5	$167.39	7.485%	$179.9191	$179.92	$179.90	$179.90
Purchase #6	$111.33	9.383%	$121.7761	$121.78	$121.80	$121.80
Purchase #7	$38.47	5.227%	$40.4808	$40.48	$40.50	$40.50
7 purchase totals =	$552.87		$590.7875	$590.80	$590.85	$590.80