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	$167.68	12.249%	$188.2191	$188.22	$188.20	$188.20
Purchase #2	$162.89	10.550%	$180.0749	$180.07	$180.05	$180.10
Purchase #3	$126.87	4.746%	$132.8913	$132.89	$132.90	$132.90
Purchase #4	$56.71	4.596%	$59.3164	$59.32	$59.30	$59.30
Purchase #5	$101.95	13.453%	$115.6653	$115.67	$115.65	$115.70
Purchase #6	$29.80	7.148%	$31.9301	$31.93	$31.95	$31.90
Purchase #7	$65.67	8.275%	$71.1042	$71.10	$71.10	$71.10
7 purchase totals =	$711.57		$779.2013	$779.20	$779.15	$779.20