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	$120.89	6.528%	$128.7817	$128.78	$128.80	$128.80
Purchase #2	$144.98	5.865%	$153.4831	$153.48	$153.50	$153.50
Purchase #3	$173.33	11.634%	$193.4952	$193.50	$193.50	$193.50
Purchase #4	$17.61	13.223%	$19.9386	$19.94	$19.95	$19.90
Purchase #5	$55.66	6.735%	$59.4087	$59.41	$59.40	$59.40
Purchase #6	$45.73	11.445%	$50.9638	$50.96	$50.95	$51.00
Purchase #7	$140.90	13.136%	$159.4086	$159.41	$159.40	$159.40
7 purchase totals =	$699.10		$765.4797	$765.48	$765.50	$765.50