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	$5.83	9.476%	$6.3825	$6.38	$6.40	$6.40
Purchase #2	$208.38	10.429%	$230.112	$230.11	$230.10	$230.10
Purchase #3	$211.51	3.695%	$219.3253	$219.33	$219.35	$219.30
Purchase #4	$242.51	3.266%	$250.4304	$250.43	$250.45	$250.40
Purchase #5	$100.87	7.854%	$108.7923	$108.79	$108.80	$108.80
Purchase #6	$229.31	7.120%	$245.6369	$245.64	$245.65	$245.60
Purchase #7	$83.53	7.669%	$89.9359	$89.94	$89.95	$89.90
7 purchase totals =	$1,081.94		$1,150.6153	$1,150.62	$1,150.70	$1,150.50