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	$40.26	4.399%	$42.031	$42.03	$42.05	$42.00
Purchase #2	$242.40	11.805%	$271.0153	$271.02	$271.00	$271.00
Purchase #3	$45.70	4.654%	$47.8269	$47.83	$47.85	$47.80
Purchase #4	$128.81	7.494%	$138.463	$138.46	$138.45	$138.50
Purchase #5	$40.39	12.780%	$45.5518	$45.55	$45.55	$45.60
Purchase #6	$142.96	5.547%	$150.89	$150.89	$150.90	$150.90
Purchase #7	$177.80	3.561%	$184.1315	$184.13	$184.15	$184.10
7 purchase totals =	$818.32		$879.9095	$879.91	$879.95	$879.90