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	$37.49	8.270%	$40.5904	$40.59	$40.60	$40.60
Purchase #2	$185.89	3.149%	$191.7437	$191.74	$191.75	$191.70
Purchase #3	$221.76	13.113%	$250.8394	$250.84	$250.85	$250.80
Purchase #4	$215.95	8.318%	$233.9127	$233.91	$233.90	$233.90
Purchase #5	$210.55	7.283%	$225.8844	$225.88	$225.90	$225.90
Purchase #6	$56.25	8.191%	$60.8574	$60.86	$60.85	$60.90
Purchase #7	$184.38	13.862%	$209.9388	$209.94	$209.95	$209.90
7 purchase totals =	$1,112.27		$1,213.7668	$1,213.76	$1,213.80	$1,213.70