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	$120.53	13.871%	$137.2487	$137.25	$137.25	$137.20
Purchase #2	$94.38	8.226%	$102.1437	$102.14	$102.15	$102.10
Purchase #3	$94.29	4.484%	$98.518	$98.52	$98.50	$98.50
Purchase #4	$228.34	9.176%	$249.2925	$249.29	$249.30	$249.30
Purchase #5	$229.40	9.822%	$251.9317	$251.93	$251.95	$251.90
Purchase #6	$161.32	4.346%	$168.331	$168.33	$168.35	$168.30
Purchase #7	$133.91	7.647%	$144.1501	$144.15	$144.15	$144.20
7 purchase totals =	$1,062.17		$1,151.6157	$1,151.61	$1,151.65	$1,151.50