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	$27.84	8.867%	$30.3086	$30.31	$30.30	$30.30
Purchase #2	$40.74	8.632%	$44.2567	$44.26	$44.25	$44.30
Purchase #3	$56.27	6.123%	$59.7154	$59.72	$59.70	$59.70
Purchase #4	$50.38	12.706%	$56.7813	$56.78	$56.80	$56.80
Purchase #5	$212.57	5.159%	$223.5365	$223.54	$223.55	$223.50
Purchase #6	$101.76	11.846%	$113.8145	$113.81	$113.80	$113.80
Purchase #7	$169.84	6.507%	$180.8915	$180.89	$180.90	$180.90
7 purchase totals =	$659.40		$709.3045	$709.31	$709.30	$709.30