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	$7.48	5.283%	$7.8752	$7.88	$7.90	$7.90
Purchase #2	$163.54	3.135%	$168.667	$168.67	$168.65	$168.70
Purchase #3	$248.50	4.123%	$258.7457	$258.75	$258.75	$258.70
Purchase #4	$245.43	10.350%	$270.832	$270.83	$270.85	$270.80
Purchase #5	$171.73	8.119%	$185.6728	$185.67	$185.65	$185.70
Purchase #6	$127.73	13.771%	$145.3197	$145.32	$145.30	$145.30
Purchase #7	$178.25	6.124%	$189.166	$189.17	$189.15	$189.20
7 purchase totals =	$1,142.66		$1,226.2784	$1,226.29	$1,226.25	$1,226.30