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	$29.98	12.127%	$33.6157	$33.62	$33.60	$33.60
Purchase #2	$152.56	11.745%	$170.4782	$170.48	$170.50	$170.50
Purchase #3	$100.95	8.192%	$109.2198	$109.22	$109.20	$109.20
Purchase #4	$245.28	4.848%	$257.1712	$257.17	$257.15	$257.20
Purchase #5	$120.94	5.836%	$127.9981	$128.00	$128.00	$128.00
Purchase #6	$115.71	13.566%	$131.4072	$131.41	$131.40	$131.40
Purchase #7	$200.42	11.507%	$223.4823	$223.48	$223.50	$223.50
7 purchase totals =	$965.84		$1,053.3725	$1,053.38	$1,053.35	$1,053.40