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	$6.61	9.799%	$7.2577	$7.26	$7.25	$7.30
Purchase #2	$113.25	12.695%	$127.6271	$127.63	$127.65	$127.60
Purchase #3	$215.85	11.301%	$240.2432	$240.24	$240.25	$240.20
Purchase #4	$86.85	3.632%	$90.0044	$90.00	$90.00	$90.00
Purchase #5	$181.28	5.559%	$191.3574	$191.36	$191.35	$191.40
Purchase #6	$50.51	11.364%	$56.25	$56.25	$56.25	$56.30
Purchase #7	$193.43	10.140%	$213.0438	$213.04	$213.05	$213.00
7 purchase totals =	$847.78		$925.7836	$925.78	$925.80	$925.80