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	$19.29	5.478%	$20.3467	$20.35	$20.35	$20.30
Purchase #2	$43.59	4.319%	$45.4727	$45.47	$45.45	$45.50
Purchase #3	$36.68	12.292%	$41.1887	$41.19	$41.20	$41.20
Purchase #4	$55.71	6.738%	$59.4637	$59.46	$59.45	$59.50
Purchase #5	$205.68	12.435%	$231.2563	$231.26	$231.25	$231.30
Purchase #6	$121.49	13.353%	$137.7126	$137.71	$137.70	$137.70
Purchase #7	$215.65	3.466%	$223.1244	$223.12	$223.10	$223.10
7 purchase totals =	$698.09		$758.5651	$758.56	$758.50	$758.60