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	$154.66	9.115%	$168.7573	$168.76	$168.75	$168.80
Purchase #2	$212.43	6.524%	$226.2889	$226.29	$226.30	$226.30
Purchase #3	$196.73	13.375%	$223.0426	$223.04	$223.05	$223.00
Purchase #4	$149.67	4.270%	$156.0609	$156.06	$156.05	$156.10
Purchase #5	$63.64	5.762%	$67.3069	$67.31	$67.30	$67.30
Purchase #6	$122.92	3.504%	$127.2271	$127.23	$127.25	$127.20
Purchase #7	$99.34	8.798%	$108.0799	$108.08	$108.10	$108.10
7 purchase totals =	$999.39		$1,076.7636	$1,076.77	$1,076.80	$1,076.80