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	$166.81	10.839%	$184.8905	$184.89	$184.90	$184.90
Purchase #2	$93.69	6.370%	$99.6581	$99.66	$99.65	$99.70
Purchase #3	$58.46	3.787%	$60.6739	$60.67	$60.65	$60.70
Purchase #4	$209.59	6.128%	$222.4337	$222.43	$222.45	$222.40
Purchase #5	$77.50	6.726%	$82.7127	$82.71	$82.70	$82.70
Purchase #6	$223.56	13.251%	$253.1839	$253.18	$253.20	$253.20
Purchase #7	$87.45	12.667%	$98.5273	$98.53	$98.55	$98.50
7 purchase totals =	$917.06		$1,002.0801	$1,002.07	$1,002.10	$1,002.10