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	$61.74	4.443%	$64.4831	$64.48	$64.50	$64.50
Purchase #2	$181.31	9.191%	$197.9742	$197.97	$197.95	$198.00
Purchase #3	$58.61	12.297%	$65.8173	$65.82	$65.80	$65.80
Purchase #4	$151.98	11.679%	$169.7297	$169.73	$169.75	$169.70
Purchase #5	$101.52	9.349%	$111.0111	$111.01	$111.00	$111.00
Purchase #6	$134.55	12.120%	$150.8575	$150.86	$150.85	$150.90
Purchase #7	$235.27	4.749%	$246.443	$246.44	$246.45	$246.40
7 purchase totals =	$924.98		$1,006.3159	$1,006.31	$1,006.30	$1,006.30