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	$34.54	7.485%	$37.1253	$37.13	$37.15	$37.10
Purchase #2	$124.74	5.383%	$131.4548	$131.45	$131.45	$131.50
Purchase #3	$207.33	7.643%	$223.1762	$223.18	$223.20	$223.20
Purchase #4	$8.83	4.523%	$9.2294	$9.23	$9.25	$9.20
Purchase #5	$47.41	12.362%	$53.2708	$53.27	$53.25	$53.30
Purchase #6	$130.61	9.104%	$142.5007	$142.50	$142.50	$142.50
Purchase #7	$5.71	12.488%	$6.4231	$6.42	$6.40	$6.40
7 purchase totals =	$559.17		$603.1803	$603.18	$603.20	$603.20