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	$53.42	7.319%	$57.3298	$57.33	$57.35	$57.30
Purchase #2	$218.85	11.347%	$243.6829	$243.68	$243.70	$243.70
Purchase #3	$73.93	11.175%	$82.1917	$82.19	$82.20	$82.20
Purchase #4	$41.92	7.282%	$44.9726	$44.97	$44.95	$45.00
Purchase #5	$247.40	3.191%	$255.2945	$255.29	$255.30	$255.30
Purchase #6	$59.77	13.614%	$67.9071	$67.91	$67.90	$67.90
Purchase #7	$53.38	8.224%	$57.77	$57.77	$57.75	$57.80
7 purchase totals =	$748.67		$809.1486	$809.14	$809.15	$809.20