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	$59.69	10.580%	$66.0052	$66.01	$66.00	$66.00
Purchase #2	$136.30	7.494%	$146.5143	$146.51	$146.50	$146.50
Purchase #3	$39.57	9.370%	$43.2777	$43.28	$43.30	$43.30
Purchase #4	$82.45	12.159%	$92.4751	$92.48	$92.50	$92.50
Purchase #5	$196.43	5.322%	$206.884	$206.88	$206.90	$206.90
Purchase #6	$71.94	6.438%	$76.5715	$76.57	$76.55	$76.60
Purchase #7	$161.40	8.255%	$174.7236	$174.72	$174.70	$174.70
7 purchase totals =	$747.78		$806.4514	$806.45	$806.45	$806.50