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	$210.32	6.334%	$223.6417	$223.64	$223.65	$223.60
Purchase #2	$142.92	10.292%	$157.6293	$157.63	$157.65	$157.60
Purchase #3	$243.65	8.627%	$264.6697	$264.67	$264.65	$264.70
Purchase #4	$74.86	4.805%	$78.457	$78.46	$78.45	$78.50
Purchase #5	$33.47	7.212%	$35.8839	$35.88	$35.90	$35.90
Purchase #6	$185.76	6.175%	$197.2307	$197.23	$197.25	$197.20
Purchase #7	$111.80	12.862%	$126.1797	$126.18	$126.20	$126.20
7 purchase totals =	$1,002.78		$1,083.6920	$1,083.69	$1,083.75	$1,083.70