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	$169.94	10.574%	$187.9095	$187.91	$187.90	$187.90
Purchase #2	$59.57	8.821%	$64.8247	$64.82	$64.80	$64.80
Purchase #3	$51.45	5.682%	$54.3734	$54.37	$54.35	$54.40
Purchase #4	$133.29	9.834%	$146.3977	$146.40	$146.40	$146.40
Purchase #5	$51.90	11.116%	$57.6692	$57.67	$57.65	$57.70
Purchase #6	$141.90	13.638%	$161.2523	$161.25	$161.25	$161.30
Purchase #7	$39.65	4.158%	$41.2986	$41.30	$41.30	$41.30
7 purchase totals =	$647.70		$713.7254	$713.72	$713.65	$713.80