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	$216.96	7.109%	$232.3837	$232.38	$232.40	$232.40
Purchase #2	$140.81	8.461%	$152.7239	$152.72	$152.70	$152.70
Purchase #3	$209.33	6.674%	$223.3007	$223.30	$223.30	$223.30
Purchase #4	$30.27	10.694%	$33.5071	$33.51	$33.50	$33.50
Purchase #5	$106.73	7.588%	$114.8287	$114.83	$114.85	$114.80
Purchase #6	$249.60	4.332%	$260.4127	$260.41	$260.40	$260.40
Purchase #7	$45.79	5.478%	$48.2984	$48.30	$48.30	$48.30
7 purchase totals =	$999.49		$1,065.4552	$1,065.45	$1,065.45	$1,065.40