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	$74.34	5.343%	$78.312	$78.31	$78.30	$78.30
Purchase #2	$197.63	7.563%	$212.5768	$212.58	$212.60	$212.60
Purchase #3	$80.71	10.801%	$89.4275	$89.43	$89.45	$89.40
Purchase #4	$6.92	12.647%	$7.7952	$7.80	$7.80	$7.80
Purchase #5	$223.69	10.138%	$246.3677	$246.37	$246.35	$246.40
Purchase #6	$229.43	9.353%	$250.8886	$250.89	$250.90	$250.90
Purchase #7	$120.58	8.671%	$131.0355	$131.04	$131.05	$131.00
7 purchase totals =	$933.30		$1,016.4033	$1,016.42	$1,016.45	$1,016.40