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	$113.80	8.867%	$123.8906	$123.89	$123.90	$123.90
Purchase #2	$249.56	12.604%	$281.0145	$281.01	$281.00	$281.00
Purchase #3	$114.45	8.750%	$124.4644	$124.46	$124.45	$124.50
Purchase #4	$50.38	9.663%	$55.2482	$55.25	$55.25	$55.20
Purchase #5	$79.74	11.632%	$89.0154	$89.02	$89.00	$89.00
Purchase #6	$26.43	9.412%	$28.9176	$28.92	$28.90	$28.90
Purchase #7	$153.28	13.601%	$174.1276	$174.13	$174.15	$174.10
7 purchase totals =	$787.64		$876.6783	$876.68	$876.65	$876.60