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	$82.74	8.762%	$89.9897	$89.99	$90.00	$90.00
Purchase #2	$146.95	13.176%	$166.3121	$166.31	$166.30	$166.30
Purchase #3	$125.28	9.226%	$136.8383	$136.84	$136.85	$136.80
Purchase #4	$152.89	6.565%	$162.9272	$162.93	$162.95	$162.90
Purchase #5	$137.34	10.151%	$151.2814	$151.28	$151.30	$151.30
Purchase #6	$109.31	3.158%	$112.762	$112.76	$112.75	$112.80
Purchase #7	$218.43	6.315%	$232.2239	$232.22	$232.20	$232.20
7 purchase totals =	$972.94		$1,052.3346	$1,052.33	$1,052.35	$1,052.30