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	$60.75	10.844%	$67.3377	$67.34	$67.35	$67.30
Purchase #2	$192.51	11.868%	$215.3571	$215.36	$215.35	$215.40
Purchase #3	$190.97	8.156%	$206.5455	$206.55	$206.55	$206.50
Purchase #4	$55.63	6.614%	$59.3094	$59.31	$59.30	$59.30
Purchase #5	$196.40	13.791%	$223.4855	$223.49	$223.50	$223.50
Purchase #6	$9.73	7.556%	$10.4652	$10.47	$10.45	$10.50
Purchase #7	$60.95	5.662%	$64.401	$64.40	$64.40	$64.40
7 purchase totals =	$766.94		$846.9014	$846.92	$846.90	$846.90