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	$60.99	12.805%	$68.7998	$68.80	$68.80	$68.80
Purchase #2	$225.60	11.834%	$252.2975	$252.30	$252.30	$252.30
Purchase #3	$88.50	12.474%	$99.5395	$99.54	$99.55	$99.50
Purchase #4	$48.29	12.873%	$54.5064	$54.51	$54.50	$54.50
Purchase #5	$213.27	9.676%	$233.906	$233.91	$233.90	$233.90
Purchase #6	$245.90	7.558%	$264.4851	$264.49	$264.50	$264.50
Purchase #7	$20.45	10.505%	$22.5983	$22.60	$22.60	$22.60
7 purchase totals =	$903.00		$996.1326	$996.15	$996.15	$996.10