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	$235.87	5.711%	$249.3405	$249.34	$249.35	$249.30
Purchase #2	$139.87	9.470%	$153.1157	$153.12	$153.10	$153.10
Purchase #3	$19.61	8.680%	$21.3121	$21.31	$21.30	$21.30
Purchase #4	$39.85	6.267%	$42.3474	$42.35	$42.35	$42.30
Purchase #5	$12.96	10.368%	$14.3037	$14.30	$14.30	$14.30
Purchase #6	$120.78	9.180%	$131.8676	$131.87	$131.85	$131.90
Purchase #7	$41.71	5.624%	$44.0558	$44.06	$44.05	$44.10
7 purchase totals =	$610.65		$656.3428	$656.35	$656.30	$656.30