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	$198.49	12.135%	$222.5768	$222.58	$222.60	$222.60
Purchase #2	$190.55	3.352%	$196.9372	$196.94	$196.95	$196.90
Purchase #3	$173.85	9.322%	$190.0563	$190.06	$190.05	$190.10
Purchase #4	$80.70	3.219%	$83.2977	$83.30	$83.30	$83.30
Purchase #5	$181.63	7.816%	$195.8262	$195.83	$195.85	$195.80
Purchase #6	$213.30	12.468%	$239.8942	$239.89	$239.90	$239.90
Purchase #7	$28.59	6.606%	$30.4787	$30.48	$30.50	$30.50
7 purchase totals =	$1,067.11		$1,159.0671	$1,159.08	$1,159.15	$1,159.10