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	$75.48	3.792%	$78.3422	$78.34	$78.35	$78.30
Purchase #2	$164.83	5.362%	$173.6682	$173.67	$173.65	$173.70
Purchase #3	$58.74	12.271%	$65.948	$65.95	$65.95	$65.90
Purchase #4	$131.37	8.819%	$142.9555	$142.96	$142.95	$143.00
Purchase #5	$59.26	13.344%	$67.1677	$67.17	$67.15	$67.20
Purchase #6	$172.41	12.526%	$194.0061	$194.01	$194.00	$194.00
Purchase #7	$39.48	11.816%	$44.145	$44.15	$44.15	$44.10
7 purchase totals =	$701.57		$766.2327	$766.25	$766.20	$766.20