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	$55.25	7.273%	$59.2683	$59.27	$59.25	$59.30
Purchase #2	$28.76	4.599%	$30.0827	$30.08	$30.10	$30.10
Purchase #3	$5.73	12.405%	$6.4408	$6.44	$6.45	$6.40
Purchase #4	$209.96	5.307%	$221.1026	$221.10	$221.10	$221.10
Purchase #5	$220.32	10.219%	$242.8345	$242.83	$242.85	$242.80
Purchase #6	$130.32	13.661%	$148.123	$148.12	$148.10	$148.10
Purchase #7	$104.48	9.601%	$114.5111	$114.51	$114.50	$114.50
7 purchase totals =	$754.82		$822.3630	$822.35	$822.35	$822.30