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	$57.52	3.287%	$59.4107	$59.41	$59.40	$59.40
Purchase #2	$32.85	3.199%	$33.9009	$33.90	$33.90	$33.90
Purchase #3	$161.30	9.392%	$176.4493	$176.45	$176.45	$176.40
Purchase #4	$67.84	12.350%	$76.2182	$76.22	$76.20	$76.20
Purchase #5	$165.61	9.865%	$181.9474	$181.95	$181.95	$181.90
Purchase #6	$142.90	5.731%	$151.0896	$151.09	$151.10	$151.10
Purchase #7	$129.87	9.599%	$142.3362	$142.34	$142.35	$142.30
7 purchase totals =	$757.89		$821.3523	$821.36	$821.35	$821.20