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	$239.77	12.149%	$268.8997	$268.90	$268.90	$268.90
Purchase #2	$210.27	11.223%	$233.8686	$233.87	$233.85	$233.90
Purchase #3	$83.79	6.437%	$89.1836	$89.18	$89.20	$89.20
Purchase #4	$85.95	3.702%	$89.1319	$89.13	$89.15	$89.10
Purchase #5	$140.97	10.663%	$156.0016	$156.00	$156.00	$156.00
Purchase #6	$53.65	3.508%	$55.532	$55.53	$55.55	$55.50
Purchase #7	$66.77	10.327%	$73.6653	$73.67	$73.65	$73.70
7 purchase totals =	$881.17		$966.2827	$966.28	$966.30	$966.30