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	$35.94	10.597%	$39.7486	$39.75	$39.75	$39.70
Purchase #2	$5.52	10.747%	$6.1132	$6.11	$6.10	$6.10
Purchase #3	$83.98	6.777%	$89.6713	$89.67	$89.65	$89.70
Purchase #4	$58.27	11.222%	$64.8091	$64.81	$64.80	$64.80
Purchase #5	$119.69	9.487%	$131.045	$131.05	$131.05	$131.00
Purchase #6	$245.39	7.345%	$263.4139	$263.41	$263.40	$263.40
Purchase #7	$19.90	6.386%	$21.1708	$21.17	$21.15	$21.20
7 purchase totals =	$568.69		$615.9719	$615.97	$615.90	$615.90