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	$152.83	12.492%	$171.9215	$171.92	$171.90	$171.90
Purchase #2	$168.98	5.596%	$178.4361	$178.44	$178.45	$178.40
Purchase #3	$199.27	12.612%	$224.4019	$224.40	$224.40	$224.40
Purchase #4	$130.27	12.401%	$146.4248	$146.42	$146.40	$146.40
Purchase #5	$67.41	10.238%	$74.3114	$74.31	$74.30	$74.30
Purchase #6	$69.66	4.308%	$72.661	$72.66	$72.65	$72.70
Purchase #7	$124.44	8.725%	$135.2974	$135.30	$135.30	$135.30
7 purchase totals =	$912.86		$1,003.4541	$1,003.45	$1,003.40	$1,003.40