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	$69.83	12.181%	$78.336	$78.34	$78.35	$78.30
Purchase #2	$145.91	10.601%	$161.3779	$161.38	$161.40	$161.40
Purchase #3	$213.42	10.839%	$236.5526	$236.55	$236.55	$236.60
Purchase #4	$210.30	6.492%	$223.9527	$223.95	$223.95	$224.00
Purchase #5	$112.73	4.774%	$118.1117	$118.11	$118.10	$118.10
Purchase #6	$224.39	11.622%	$250.4686	$250.47	$250.45	$250.50
Purchase #7	$227.52	11.627%	$253.9738	$253.97	$253.95	$254.00
7 purchase totals =	$1,204.10		$1,322.7733	$1,322.77	$1,322.75	$1,322.90