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	$68.89	13.253%	$78.02	$78.02	$78.00	$78.00
Purchase #2	$152.43	10.486%	$168.4138	$168.41	$168.40	$168.40
Purchase #3	$99.68	11.614%	$111.2568	$111.26	$111.25	$111.30
Purchase #4	$25.93	3.486%	$26.8339	$26.83	$26.85	$26.80
Purchase #5	$27.92	9.795%	$30.6548	$30.65	$30.65	$30.70
Purchase #6	$84.66	6.160%	$89.8751	$89.88	$89.90	$89.90
Purchase #7	$184.46	6.332%	$196.14	$196.14	$196.15	$196.10
7 purchase totals =	$643.97		$701.1944	$701.19	$701.20	$701.20