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	$36.54	11.859%	$40.8733	$40.87	$40.85	$40.90
Purchase #2	$81.90	11.589%	$91.3914	$91.39	$91.40	$91.40
Purchase #3	$31.35	6.655%	$33.4363	$33.44	$33.45	$33.40
Purchase #4	$249.83	3.599%	$258.8214	$258.82	$258.80	$258.80
Purchase #5	$233.96	13.222%	$264.8942	$264.89	$264.90	$264.90
Purchase #6	$80.72	4.180%	$84.0941	$84.09	$84.10	$84.10
Purchase #7	$92.97	8.321%	$100.706	$100.71	$100.70	$100.70
7 purchase totals =	$807.27		$874.2167	$874.21	$874.20	$874.20