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	$29.82	5.217%	$31.3757	$31.38	$31.40	$31.40
Purchase #2	$59.65	9.585%	$65.3675	$65.37	$65.35	$65.40
Purchase #3	$27.85	5.682%	$29.4324	$29.43	$29.45	$29.40
Purchase #4	$88.27	9.216%	$96.405	$96.41	$96.40	$96.40
Purchase #5	$24.76	13.650%	$28.1397	$28.14	$28.15	$28.10
Purchase #6	$151.65	4.139%	$157.9268	$157.93	$157.95	$157.90
Purchase #7	$182.80	7.316%	$196.1736	$196.17	$196.15	$196.20
7 purchase totals =	$564.80		$604.8207	$604.83	$604.85	$604.80