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	$98.90	10.390%	$109.1757	$109.18	$109.20	$109.20
Purchase #2	$97.48	3.373%	$100.768	$100.77	$100.75	$100.80
Purchase #3	$8.34	11.804%	$9.3245	$9.32	$9.30	$9.30
Purchase #4	$200.64	4.436%	$209.5404	$209.54	$209.55	$209.50
Purchase #5	$96.29	3.339%	$99.5051	$99.51	$99.50	$99.50
Purchase #6	$56.93	13.423%	$64.5717	$64.57	$64.55	$64.60
Purchase #7	$26.99	4.313%	$28.1541	$28.15	$28.15	$28.20
7 purchase totals =	$585.57		$621.0395	$621.04	$621.00	$621.10