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	$19.79	8.835%	$21.5384	$21.54	$21.55	$21.50
Purchase #2	$37.51	6.305%	$39.875	$39.88	$39.90	$39.90
Purchase #3	$12.84	7.689%	$13.8273	$13.83	$13.85	$13.80
Purchase #4	$80.57	8.363%	$87.3081	$87.31	$87.30	$87.30
Purchase #5	$46.75	13.679%	$53.1449	$53.14	$53.15	$53.10
Purchase #6	$119.54	10.173%	$131.7008	$131.70	$131.70	$131.70
Purchase #7	$37.30	7.524%	$40.1065	$40.11	$40.10	$40.10
7 purchase totals =	$354.30		$387.5010	$387.51	$387.55	$387.40