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	$57.73	6.144%	$61.2769	$61.28	$61.30	$61.30
Purchase #2	$103.90	7.730%	$111.9315	$111.93	$111.95	$111.90
Purchase #3	$110.32	4.811%	$115.6275	$115.63	$115.65	$115.60
Purchase #4	$69.72	4.351%	$72.7535	$72.75	$72.75	$72.80
Purchase #5	$159.75	4.609%	$167.1129	$167.11	$167.10	$167.10
Purchase #6	$96.91	5.574%	$102.3118	$102.31	$102.30	$102.30
Purchase #7	$45.87	12.826%	$51.7533	$51.75	$51.75	$51.80
7 purchase totals =	$644.20		$682.7674	$682.76	$682.80	$682.80