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	$73.50	7.337%	$78.8927	$78.89	$78.90	$78.90
Purchase #2	$134.96	12.834%	$152.2808	$152.28	$152.30	$152.30
Purchase #3	$145.35	10.584%	$160.7338	$160.73	$160.75	$160.70
Purchase #4	$131.64	9.741%	$144.4631	$144.46	$144.45	$144.50
Purchase #5	$82.91	9.338%	$90.6521	$90.65	$90.65	$90.70
Purchase #6	$43.28	13.346%	$49.0561	$49.06	$49.05	$49.10
Purchase #7	$82.66	4.450%	$86.3384	$86.34	$86.35	$86.30
7 purchase totals =	$694.30		$762.4170	$762.41	$762.45	$762.50