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	$45.68	11.563%	$50.962	$50.96	$50.95	$51.00
Purchase #2	$230.53	10.276%	$254.2193	$254.22	$254.20	$254.20
Purchase #3	$115.32	13.619%	$131.0254	$131.03	$131.05	$131.00
Purchase #4	$123.77	11.419%	$137.9033	$137.90	$137.90	$137.90
Purchase #5	$152.64	9.754%	$167.5285	$167.53	$167.55	$167.50
Purchase #6	$146.34	13.814%	$166.5554	$166.56	$166.55	$166.60
Purchase #7	$236.51	11.626%	$264.0067	$264.01	$264.00	$264.00
7 purchase totals =	$1,050.79		$1,172.2006	$1,172.21	$1,172.20	$1,172.20