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	$237.79	5.280%	$250.3453	$250.35	$250.35	$250.30
Purchase #2	$151.90	11.142%	$168.8247	$168.82	$168.80	$168.80
Purchase #3	$19.96	6.479%	$21.2532	$21.25	$21.25	$21.30
Purchase #4	$197.29	12.713%	$222.3715	$222.37	$222.35	$222.40
Purchase #5	$174.63	10.694%	$193.3049	$193.30	$193.30	$193.30
Purchase #6	$106.32	11.618%	$118.6723	$118.67	$118.65	$118.70
Purchase #7	$134.56	10.701%	$148.9593	$148.96	$148.95	$149.00
7 purchase totals =	$1,022.45		$1,123.7312	$1,123.72	$1,123.65	$1,123.80