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	$249.52	9.451%	$273.1021	$273.10	$273.10	$273.10
Purchase #2	$111.26	3.803%	$115.4912	$115.49	$115.50	$115.50
Purchase #3	$116.25	3.211%	$119.9828	$119.98	$120.00	$120.00
Purchase #4	$220.71	12.717%	$248.7777	$248.78	$248.80	$248.80
Purchase #5	$81.83	10.467%	$90.3951	$90.40	$90.40	$90.40
Purchase #6	$20.56	10.441%	$22.7067	$22.71	$22.70	$22.70
Purchase #7	$59.41	3.390%	$61.424	$61.42	$61.40	$61.40
7 purchase totals =	$859.54		$931.8796	$931.88	$931.90	$931.90