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	$139.89	5.406%	$147.4525	$147.45	$147.45	$147.50
Purchase #2	$103.49	5.507%	$109.1892	$109.19	$109.20	$109.20
Purchase #3	$222.41	6.569%	$237.0201	$237.02	$237.00	$237.00
Purchase #4	$16.35	10.186%	$18.0154	$18.02	$18.00	$18.00
Purchase #5	$57.36	3.330%	$59.2701	$59.27	$59.25	$59.30
Purchase #6	$156.31	3.817%	$162.2764	$162.28	$162.30	$162.30
Purchase #7	$90.31	8.352%	$97.8527	$97.85	$97.85	$97.90
7 purchase totals =	$786.12		$831.0764	$831.08	$831.05	$831.20