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	$83.63	7.816%	$90.1665	$90.17	$90.15	$90.20
Purchase #2	$21.65	13.208%	$24.5095	$24.51	$24.50	$24.50
Purchase #3	$192.92	8.830%	$209.9548	$209.95	$209.95	$210.00
Purchase #4	$182.30	6.278%	$193.7448	$193.74	$193.75	$193.70
Purchase #5	$140.64	13.690%	$159.8936	$159.89	$159.90	$159.90
Purchase #6	$41.27	7.356%	$44.3058	$44.31	$44.30	$44.30
Purchase #7	$55.48	12.179%	$62.2369	$62.24	$62.25	$62.20
7 purchase totals =	$717.89		$784.8119	$784.81	$784.80	$784.80