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	$156.59	9.340%	$171.2155	$171.22	$171.20	$171.20
Purchase #2	$91.97	13.709%	$104.5782	$104.58	$104.60	$104.60
Purchase #3	$60.36	11.645%	$67.3889	$67.39	$67.40	$67.40
Purchase #4	$231.40	10.140%	$254.864	$254.86	$254.85	$254.90
Purchase #5	$5.94	7.481%	$6.3844	$6.38	$6.40	$6.40
Purchase #6	$39.68	9.536%	$43.4639	$43.46	$43.45	$43.50
Purchase #7	$241.27	10.834%	$267.4092	$267.41	$267.40	$267.40
7 purchase totals =	$827.21		$915.3041	$915.30	$915.30	$915.40