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	$84.61	7.272%	$90.7628	$90.76	$90.75	$90.80
Purchase #2	$32.43	13.226%	$36.7192	$36.72	$36.70	$36.70
Purchase #3	$79.71	7.147%	$85.4069	$85.41	$85.40	$85.40
Purchase #4	$136.94	13.492%	$155.4159	$155.42	$155.40	$155.40
Purchase #5	$112.81	6.815%	$120.498	$120.50	$120.50	$120.50
Purchase #6	$135.54	3.415%	$140.1687	$140.17	$140.15	$140.20
Purchase #7	$133.35	13.791%	$151.7403	$151.74	$151.75	$151.70
7 purchase totals =	$715.39		$780.7118	$780.72	$780.65	$780.70