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	$55.82	6.492%	$59.4438	$59.44	$59.45	$59.40
Purchase #2	$181.56	5.499%	$191.544	$191.54	$191.55	$191.50
Purchase #3	$148.95	9.358%	$162.8887	$162.89	$162.90	$162.90
Purchase #4	$127.91	7.811%	$137.9011	$137.90	$137.90	$137.90
Purchase #5	$103.72	3.711%	$107.569	$107.57	$107.55	$107.60
Purchase #6	$9.30	13.427%	$10.5487	$10.55	$10.55	$10.50
Purchase #7	$124.50	11.195%	$138.4378	$138.44	$138.45	$138.40
7 purchase totals =	$751.76		$808.3331	$808.33	$808.35	$808.20