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	$19.58	5.274%	$20.6126	$20.61	$20.60	$20.60
Purchase #2	$53.70	11.538%	$59.8959	$59.90	$59.90	$59.90
Purchase #3	$73.52	9.220%	$80.2985	$80.30	$80.30	$80.30
Purchase #4	$216.43	12.299%	$243.0487	$243.05	$243.05	$243.00
Purchase #5	$214.37	11.207%	$238.3944	$238.39	$238.40	$238.40
Purchase #6	$15.39	13.538%	$17.4735	$17.47	$17.45	$17.50
Purchase #7	$24.31	11.543%	$27.1161	$27.12	$27.10	$27.10
7 purchase totals =	$617.30		$686.8397	$686.84	$686.80	$686.80