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	$135.27	12.521%	$152.2072	$152.21	$152.20	$152.20
Purchase #2	$137.99	13.456%	$156.5579	$156.56	$156.55	$156.60
Purchase #3	$79.74	12.557%	$89.753	$89.75	$89.75	$89.80
Purchase #4	$47.42	7.423%	$50.94	$50.94	$50.95	$50.90
Purchase #5	$48.83	11.682%	$54.5343	$54.53	$54.55	$54.50
Purchase #6	$38.80	8.202%	$41.9824	$41.98	$42.00	$42.00
Purchase #7	$104.84	4.207%	$109.2506	$109.25	$109.25	$109.30
7 purchase totals =	$592.89		$655.2254	$655.22	$655.25	$655.30