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	$24.75	3.225%	$25.5482	$25.55	$25.55	$25.50
Purchase #2	$192.92	12.178%	$216.4138	$216.41	$216.40	$216.40
Purchase #3	$69.55	12.655%	$78.3516	$78.35	$78.35	$78.40
Purchase #4	$216.91	12.705%	$244.4684	$244.47	$244.45	$244.50
Purchase #5	$146.59	4.800%	$153.6263	$153.63	$153.65	$153.60
Purchase #6	$234.43	10.676%	$259.4577	$259.46	$259.45	$259.50
Purchase #7	$115.90	8.219%	$125.4258	$125.43	$125.45	$125.40
7 purchase totals =	$1,001.05		$1,103.2918	$1,103.30	$1,103.30	$1,103.30