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	$104.43	6.169%	$110.8723	$110.87	$110.85	$110.90
Purchase #2	$95.79	11.608%	$106.9093	$106.91	$106.90	$106.90
Purchase #3	$213.52	12.205%	$239.5801	$239.58	$239.60	$239.60
Purchase #4	$57.64	3.232%	$59.5029	$59.50	$59.50	$59.50
Purchase #5	$184.69	8.654%	$200.6731	$200.67	$200.65	$200.70
Purchase #6	$92.77	7.296%	$99.5385	$99.54	$99.55	$99.50
Purchase #7	$47.92	11.245%	$53.3086	$53.31	$53.30	$53.30
7 purchase totals =	$796.76		$870.3848	$870.38	$870.35	$870.40