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	$100.53	12.509%	$113.1053	$113.11	$113.10	$113.10
Purchase #2	$123.90	13.283%	$140.3576	$140.36	$140.35	$140.40
Purchase #3	$14.49	13.260%	$16.4114	$16.41	$16.40	$16.40
Purchase #4	$55.73	6.602%	$59.4093	$59.41	$59.40	$59.40
Purchase #5	$99.28	4.522%	$103.7694	$103.77	$103.75	$103.80
Purchase #6	$139.39	9.164%	$152.1637	$152.16	$152.15	$152.20
Purchase #7	$68.63	3.566%	$71.0773	$71.08	$71.10	$71.10
7 purchase totals =	$601.95		$656.2940	$656.30	$656.25	$656.40