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	$73.81	12.323%	$82.9056	$82.91	$82.90	$82.90
Purchase #2	$165.99	9.456%	$181.686	$181.69	$181.70	$181.70
Purchase #3	$18.40	13.548%	$20.8928	$20.89	$20.90	$20.90
Purchase #4	$45.50	6.732%	$48.5631	$48.56	$48.55	$48.60
Purchase #5	$128.30	10.524%	$141.8023	$141.80	$141.80	$141.80
Purchase #6	$149.90	12.585%	$168.7649	$168.76	$168.75	$168.80
Purchase #7	$24.74	4.687%	$25.8996	$25.90	$25.90	$25.90
7 purchase totals =	$606.64		$670.5143	$670.51	$670.50	$670.60