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	$79.79	12.179%	$89.5076	$89.51	$89.50	$89.50
Purchase #2	$164.40	10.859%	$182.2522	$182.25	$182.25	$182.30
Purchase #3	$70.94	12.867%	$80.0678	$80.07	$80.05	$80.10
Purchase #4	$186.28	6.226%	$197.8778	$197.88	$197.90	$197.90
Purchase #5	$244.92	8.121%	$264.81	$264.81	$264.80	$264.80
Purchase #6	$181.88	5.720%	$192.2835	$192.28	$192.30	$192.30
Purchase #7	$88.61	4.799%	$92.8624	$92.86	$92.85	$92.90
7 purchase totals =	$1,016.82		$1,099.6613	$1,099.66	$1,099.65	$1,099.80