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	$88.41	12.666%	$99.608	$99.61	$99.60	$99.60
Purchase #2	$234.52	5.425%	$247.2427	$247.24	$247.25	$247.20
Purchase #3	$202.39	11.356%	$225.3734	$225.37	$225.35	$225.40
Purchase #4	$161.69	13.632%	$183.7316	$183.73	$183.75	$183.70
Purchase #5	$13.41	10.569%	$14.8273	$14.83	$14.85	$14.80
Purchase #6	$35.85	7.146%	$38.4118	$38.41	$38.40	$38.40
Purchase #7	$41.32	3.829%	$42.9021	$42.90	$42.90	$42.90
7 purchase totals =	$777.59		$852.0969	$852.09	$852.10	$852.00