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	$229.47	5.687%	$242.52	$242.52	$242.50	$242.50
Purchase #2	$165.81	11.719%	$185.2413	$185.24	$185.25	$185.20
Purchase #3	$37.25	7.416%	$40.0125	$40.01	$40.00	$40.00
Purchase #4	$22.77	9.865%	$25.0163	$25.02	$25.00	$25.00
Purchase #5	$67.96	12.412%	$76.3952	$76.40	$76.40	$76.40
Purchase #6	$177.74	10.785%	$196.9093	$196.91	$196.90	$196.90
Purchase #7	$39.50	3.209%	$40.7676	$40.77	$40.75	$40.80
7 purchase totals =	$740.50		$806.8622	$806.87	$806.80	$806.80