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	$123.64	10.692%	$136.8596	$136.86	$136.85	$136.90
Purchase #2	$85.48	13.116%	$96.6916	$96.69	$96.70	$96.70
Purchase #3	$130.34	12.596%	$146.7576	$146.76	$146.75	$146.80
Purchase #4	$9.51	7.834%	$10.255	$10.26	$10.25	$10.30
Purchase #5	$211.82	6.112%	$224.7664	$224.77	$224.75	$224.80
Purchase #6	$91.58	13.366%	$103.8206	$103.82	$103.80	$103.80
Purchase #7	$42.50	7.673%	$45.761	$45.76	$45.75	$45.80
7 purchase totals =	$694.87		$764.9118	$764.92	$764.85	$765.10