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	$153.65	12.443%	$172.7687	$172.77	$172.75	$172.80
Purchase #2	$47.33	12.210%	$53.109	$53.11	$53.10	$53.10
Purchase #3	$203.25	12.457%	$228.5689	$228.57	$228.55	$228.60
Purchase #4	$193.37	11.537%	$215.6791	$215.68	$215.70	$215.70
Purchase #5	$25.63	11.534%	$28.5862	$28.59	$28.60	$28.60
Purchase #6	$55.27	8.342%	$59.8806	$59.88	$59.90	$59.90
Purchase #7	$179.99	11.201%	$200.1507	$200.15	$200.15	$200.20
7 purchase totals =	$858.49		$958.7432	$958.75	$958.75	$958.90