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	$27.70	7.757%	$29.8487	$29.85	$29.85	$29.80
Purchase #2	$106.72	7.665%	$114.9001	$114.90	$114.90	$114.90
Purchase #3	$92.69	7.681%	$99.8095	$99.81	$99.80	$99.80
Purchase #4	$155.40	7.486%	$167.0332	$167.03	$167.05	$167.00
Purchase #5	$124.61	12.168%	$139.7725	$139.77	$139.75	$139.80
Purchase #6	$95.25	11.214%	$105.9313	$105.93	$105.95	$105.90
Purchase #7	$41.29	11.597%	$46.0784	$46.08	$46.10	$46.10
7 purchase totals =	$643.66		$703.3737	$703.37	$703.40	$703.30