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	$203.55	6.200%	$216.1701	$216.17	$216.15	$216.20
Purchase #2	$89.72	13.223%	$101.5837	$101.58	$101.60	$101.60
Purchase #3	$5.70	7.315%	$6.117	$6.12	$6.10	$6.10
Purchase #4	$201.35	10.582%	$222.6569	$222.66	$222.65	$222.70
Purchase #5	$94.31	6.436%	$100.3798	$100.38	$100.40	$100.40
Purchase #6	$130.51	7.646%	$140.4888	$140.49	$140.50	$140.50
Purchase #7	$43.76	13.706%	$49.7577	$49.76	$49.75	$49.80
7 purchase totals =	$768.90		$837.1540	$837.16	$837.15	$837.30