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	$134.51	12.522%	$151.3533	$151.35	$151.35	$151.40
Purchase #2	$21.50	6.443%	$22.8852	$22.89	$22.90	$22.90
Purchase #3	$230.63	4.654%	$241.3635	$241.36	$241.35	$241.40
Purchase #4	$52.49	13.428%	$59.5384	$59.54	$59.55	$59.50
Purchase #5	$123.99	3.820%	$128.7264	$128.73	$128.75	$128.70
Purchase #6	$170.55	13.630%	$193.796	$193.80	$193.80	$193.80
Purchase #7	$35.41	13.591%	$40.2226	$40.22	$40.20	$40.20
7 purchase totals =	$769.08		$837.8854	$837.89	$837.90	$837.90