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	$8.87	10.186%	$9.7735	$9.77	$9.75	$9.80
Purchase #2	$160.50	11.639%	$179.1806	$179.18	$179.20	$179.20
Purchase #3	$17.28	7.115%	$18.5095	$18.51	$18.50	$18.50
Purchase #4	$176.73	10.550%	$195.375	$195.38	$195.40	$195.40
Purchase #5	$89.39	12.661%	$100.7077	$100.71	$100.70	$100.70
Purchase #6	$59.71	5.860%	$63.209	$63.21	$63.20	$63.20
Purchase #7	$72.42	8.360%	$78.4743	$78.47	$78.45	$78.50
7 purchase totals =	$584.90		$645.2296	$645.23	$645.20	$645.30