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	$223.31	13.396%	$253.2246	$253.22	$253.20	$253.20
Purchase #2	$108.99	9.844%	$119.719	$119.72	$119.70	$119.70
Purchase #3	$95.25	4.258%	$99.3057	$99.31	$99.30	$99.30
Purchase #4	$175.94	11.781%	$196.6675	$196.67	$196.65	$196.70
Purchase #5	$135.82	4.860%	$142.4209	$142.42	$142.40	$142.40
Purchase #6	$90.96	5.623%	$96.0747	$96.07	$96.05	$96.10
Purchase #7	$132.90	12.631%	$149.6866	$149.69	$149.70	$149.70
7 purchase totals =	$963.17		$1,057.0990	$1,057.10	$1,057.00	$1,057.10