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	$62.78	13.177%	$71.0525	$71.05	$71.05	$71.10
Purchase #2	$155.34	6.148%	$164.8903	$164.89	$164.90	$164.90
Purchase #3	$204.92	7.122%	$219.5144	$219.51	$219.50	$219.50
Purchase #4	$175.83	3.564%	$182.0966	$182.10	$182.10	$182.10
Purchase #5	$45.76	6.215%	$48.604	$48.60	$48.60	$48.60
Purchase #6	$82.62	8.818%	$89.9054	$89.91	$89.90	$89.90
Purchase #7	$173.40	12.657%	$195.3472	$195.35	$195.35	$195.30
7 purchase totals =	$900.65		$971.4104	$971.41	$971.40	$971.40