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	$120.57	11.861%	$134.8708	$134.87	$134.85	$134.90
Purchase #2	$147.48	8.837%	$160.5128	$160.51	$160.50	$160.50
Purchase #3	$59.50	13.201%	$67.3546	$67.35	$67.35	$67.40
Purchase #4	$52.90	3.765%	$54.8917	$54.89	$54.90	$54.90
Purchase #5	$198.72	10.236%	$219.061	$219.06	$219.05	$219.10
Purchase #6	$123.71	11.485%	$137.9181	$137.92	$137.90	$137.90
Purchase #7	$160.54	8.510%	$174.202	$174.20	$174.20	$174.20
7 purchase totals =	$863.42		$948.8110	$948.80	$948.75	$948.90