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	$78.31	5.628%	$82.7173	$82.72	$82.70	$82.70
Purchase #2	$53.46	13.469%	$60.6605	$60.66	$60.65	$60.70
Purchase #3	$118.90	7.756%	$128.1219	$128.12	$128.10	$128.10
Purchase #4	$146.71	3.165%	$151.3534	$151.35	$151.35	$151.40
Purchase #5	$84.72	3.742%	$87.8902	$87.89	$87.90	$87.90
Purchase #6	$82.31	4.178%	$85.7489	$85.75	$85.75	$85.70
Purchase #7	$79.28	7.688%	$85.375	$85.38	$85.40	$85.40
7 purchase totals =	$643.69		$681.8672	$681.87	$681.85	$681.90