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	$166.44	12.507%	$187.2567	$187.26	$187.25	$187.30
Purchase #2	$127.88	7.443%	$137.3981	$137.40	$137.40	$137.40
Purchase #3	$166.52	3.792%	$172.8344	$172.83	$172.85	$172.80
Purchase #4	$85.85	6.377%	$91.3247	$91.32	$91.30	$91.30
Purchase #5	$129.57	9.842%	$142.3223	$142.32	$142.30	$142.30
Purchase #6	$27.55	8.149%	$29.795	$29.80	$29.80	$29.80
Purchase #7	$37.90	7.197%	$40.6277	$40.63	$40.65	$40.60
7 purchase totals =	$741.71		$801.5589	$801.56	$801.55	$801.50