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	$69.39	12.115%	$77.7966	$77.80	$77.80	$77.80
Purchase #2	$79.71	12.637%	$89.783	$89.78	$89.80	$89.80
Purchase #3	$65.36	7.381%	$70.1842	$70.18	$70.20	$70.20
Purchase #4	$214.49	3.758%	$222.5505	$222.55	$222.55	$222.60
Purchase #5	$62.27	8.175%	$67.3606	$67.36	$67.35	$67.40
Purchase #6	$42.30	7.591%	$45.511	$45.51	$45.50	$45.50
Purchase #7	$128.39	9.768%	$140.9311	$140.93	$140.95	$140.90
7 purchase totals =	$661.91		$714.1170	$714.11	$714.15	$714.20