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	$90.75	11.614%	$101.2897	$101.29	$101.30	$101.30
Purchase #2	$82.90	7.385%	$89.0222	$89.02	$89.00	$89.00
Purchase #3	$191.28	7.407%	$205.4481	$205.45	$205.45	$205.40
Purchase #4	$65.81	3.647%	$68.2101	$68.21	$68.20	$68.20
Purchase #5	$143.63	4.617%	$150.2614	$150.26	$150.25	$150.30
Purchase #6	$57.35	7.758%	$61.7992	$61.80	$61.80	$61.80
Purchase #7	$144.69	7.276%	$155.2176	$155.22	$155.20	$155.20
7 purchase totals =	$776.41		$831.2483	$831.25	$831.20	$831.20