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	$115.33	13.873%	$131.3297	$131.33	$131.35	$131.30
Purchase #2	$129.37	13.177%	$146.4171	$146.42	$146.40	$146.40
Purchase #3	$73.41	13.251%	$83.1376	$83.14	$83.15	$83.10
Purchase #4	$98.75	6.800%	$105.465	$105.47	$105.45	$105.50
Purchase #5	$78.30	9.829%	$85.9961	$86.00	$86.00	$86.00
Purchase #6	$26.77	6.483%	$28.5055	$28.51	$28.50	$28.50
Purchase #7	$210.93	13.200%	$238.7728	$238.77	$238.75	$238.80
7 purchase totals =	$732.86		$819.6238	$819.64	$819.60	$819.60