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	$127.82	6.751%	$136.4491	$136.45	$136.45	$136.40
Purchase #2	$138.32	7.418%	$148.5806	$148.58	$148.60	$148.60
Purchase #3	$158.41	8.324%	$171.596	$171.60	$171.60	$171.60
Purchase #4	$249.36	6.627%	$265.8851	$265.89	$265.90	$265.90
Purchase #5	$85.28	4.118%	$88.7918	$88.79	$88.80	$88.80
Purchase #6	$159.54	10.467%	$176.2391	$176.24	$176.25	$176.20
Purchase #7	$90.34	9.306%	$98.747	$98.75	$98.75	$98.70
7 purchase totals =	$1,009.07		$1,086.2887	$1,086.30	$1,086.35	$1,086.20