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	$162.60	10.438%	$179.5722	$179.57	$179.55	$179.60
Purchase #2	$79.45	11.436%	$88.5359	$88.54	$88.55	$88.50
Purchase #3	$129.65	10.377%	$143.1038	$143.10	$143.10	$143.10
Purchase #4	$225.39	6.171%	$239.2988	$239.30	$239.30	$239.30
Purchase #5	$189.96	13.624%	$215.8402	$215.84	$215.85	$215.80
Purchase #6	$93.30	6.136%	$99.0249	$99.02	$99.00	$99.00
Purchase #7	$233.69	10.450%	$258.1106	$258.11	$258.10	$258.10
7 purchase totals =	$1,114.04		$1,223.4864	$1,223.48	$1,223.45	$1,223.40