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	$46.76	9.331%	$51.1232	$51.12	$51.10	$51.10
Purchase #2	$172.56	11.199%	$191.885	$191.89	$191.90	$191.90
Purchase #3	$155.80	11.211%	$173.2667	$173.27	$173.25	$173.30
Purchase #4	$7.86	9.483%	$8.6054	$8.61	$8.60	$8.60
Purchase #5	$15.31	8.240%	$16.5715	$16.57	$16.55	$16.60
Purchase #6	$55.47	7.683%	$59.7318	$59.73	$59.75	$59.70
Purchase #7	$161.75	12.288%	$181.6258	$181.63	$181.65	$181.60
7 purchase totals =	$615.51		$682.8094	$682.82	$682.80	$682.80