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	$164.32	13.139%	$185.91	$185.91	$185.90	$185.90
Purchase #2	$78.25	6.210%	$83.1093	$83.11	$83.10	$83.10
Purchase #3	$224.48	13.356%	$254.4615	$254.46	$254.45	$254.50
Purchase #4	$231.73	5.429%	$244.3106	$244.31	$244.30	$244.30
Purchase #5	$219.87	6.372%	$233.8801	$233.88	$233.90	$233.90
Purchase #6	$48.33	7.624%	$52.0147	$52.01	$52.00	$52.00
Purchase #7	$170.80	5.169%	$179.6287	$179.63	$179.65	$179.60
7 purchase totals =	$1,137.78		$1,233.3149	$1,233.31	$1,233.30	$1,233.30