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	$237.70	11.434%	$264.8786	$264.88	$264.90	$264.90
Purchase #2	$158.56	13.504%	$179.9719	$179.97	$179.95	$180.00
Purchase #3	$165.68	12.871%	$187.0047	$187.00	$187.00	$187.00
Purchase #4	$66.30	6.179%	$70.3967	$70.40	$70.40	$70.40
Purchase #5	$50.82	13.448%	$57.6543	$57.65	$57.65	$57.70
Purchase #6	$137.49	5.748%	$145.3929	$145.39	$145.40	$145.40
Purchase #7	$174.48	6.304%	$185.4792	$185.48	$185.50	$185.50
7 purchase totals =	$991.03		$1,090.7783	$1,090.77	$1,090.80	$1,090.90