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	$139.52	9.137%	$152.2679	$152.27	$152.25	$152.30
Purchase #2	$78.76	8.140%	$85.1711	$85.17	$85.15	$85.20
Purchase #3	$245.48	8.170%	$265.5357	$265.54	$265.55	$265.50
Purchase #4	$41.30	3.837%	$42.8847	$42.88	$42.90	$42.90
Purchase #5	$105.45	13.803%	$120.0053	$120.01	$120.00	$120.00
Purchase #6	$187.42	12.725%	$211.2692	$211.27	$211.25	$211.30
Purchase #7	$232.25	5.320%	$244.6057	$244.61	$244.60	$244.60
7 purchase totals =	$1,030.18		$1,121.7396	$1,121.75	$1,121.70	$1,121.80