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	$45.28	11.167%	$50.3364	$50.34	$50.35	$50.30
Purchase #2	$62.80	6.115%	$66.6402	$66.64	$66.65	$66.60
Purchase #3	$67.93	6.781%	$72.5363	$72.54	$72.55	$72.50
Purchase #4	$44.59	7.158%	$47.7818	$47.78	$47.80	$47.80
Purchase #5	$173.46	5.844%	$183.597	$183.60	$183.60	$183.60
Purchase #6	$22.56	12.401%	$25.3577	$25.36	$25.35	$25.40
Purchase #7	$99.53	6.264%	$105.7646	$105.76	$105.75	$105.80
7 purchase totals =	$516.15		$552.0140	$552.02	$552.05	$552.00