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	$90.44	9.488%	$99.0209	$99.02	$99.00	$99.00
Purchase #2	$113.36	8.754%	$123.2835	$123.28	$123.30	$123.30
Purchase #3	$122.53	11.714%	$136.8832	$136.88	$136.90	$136.90
Purchase #4	$146.99	13.479%	$166.8028	$166.80	$166.80	$166.80
Purchase #5	$162.43	3.680%	$168.4074	$168.41	$168.40	$168.40
Purchase #6	$70.89	9.324%	$77.4998	$77.50	$77.50	$77.50
Purchase #7	$53.84	6.493%	$57.3358	$57.34	$57.35	$57.30
7 purchase totals =	$760.48		$829.2334	$829.23	$829.25	$829.20