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	$63.75	13.309%	$72.2345	$72.23	$72.25	$72.20
Purchase #2	$22.86	9.856%	$25.1131	$25.11	$25.10	$25.10
Purchase #3	$249.60	10.828%	$276.6267	$276.63	$276.65	$276.60
Purchase #4	$124.50	4.850%	$130.5383	$130.54	$130.55	$130.50
Purchase #5	$99.31	12.641%	$111.8638	$111.86	$111.85	$111.90
Purchase #6	$202.63	6.250%	$215.2944	$215.29	$215.30	$215.30
Purchase #7	$245.45	9.586%	$268.9788	$268.98	$269.00	$269.00
7 purchase totals =	$1,008.10		$1,100.6496	$1,100.64	$1,100.70	$1,100.60