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	$231.27	9.796%	$253.9252	$253.93	$253.95	$253.90
Purchase #2	$133.85	7.479%	$143.8606	$143.86	$143.85	$143.90
Purchase #3	$234.77	7.180%	$251.6265	$251.63	$251.65	$251.60
Purchase #4	$109.28	9.847%	$120.0408	$120.04	$120.05	$120.00
Purchase #5	$98.75	13.195%	$111.7801	$111.78	$111.80	$111.80
Purchase #6	$162.86	7.450%	$174.9931	$174.99	$175.00	$175.00
Purchase #7	$61.26	10.402%	$67.6323	$67.63	$67.65	$67.60
7 purchase totals =	$1,032.04		$1,123.8586	$1,123.86	$1,123.95	$1,123.80