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	$87.74	5.675%	$92.7192	$92.72	$92.70	$92.70
Purchase #2	$222.46	12.779%	$250.8882	$250.89	$250.90	$250.90
Purchase #3	$236.82	9.760%	$259.9336	$259.93	$259.95	$259.90
Purchase #4	$187.81	11.523%	$209.4513	$209.45	$209.45	$209.50
Purchase #5	$92.82	4.330%	$96.8391	$96.84	$96.85	$96.80
Purchase #6	$230.69	5.819%	$244.1139	$244.11	$244.10	$244.10
Purchase #7	$40.62	11.210%	$45.1735	$45.17	$45.15	$45.20
7 purchase totals =	$1,098.96		$1,199.1188	$1,199.11	$1,199.10	$1,199.10