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	$122.88	6.709%	$131.124	$131.12	$131.10	$131.10
Purchase #2	$220.93	13.555%	$250.8771	$250.88	$250.90	$250.90
Purchase #3	$214.60	3.244%	$221.5616	$221.56	$221.55	$221.60
Purchase #4	$52.80	6.370%	$56.1634	$56.16	$56.15	$56.20
Purchase #5	$42.33	10.659%	$46.842	$46.84	$46.85	$46.80
Purchase #6	$246.36	7.307%	$264.3615	$264.36	$264.35	$264.40
Purchase #7	$74.79	10.335%	$82.5195	$82.52	$82.50	$82.50
7 purchase totals =	$974.69		$1,053.4491	$1,053.44	$1,053.40	$1,053.50