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	$130.43	12.718%	$147.0181	$147.02	$147.00	$147.00
Purchase #2	$91.34	9.838%	$100.326	$100.33	$100.35	$100.30
Purchase #3	$74.89	6.813%	$79.9923	$79.99	$80.00	$80.00
Purchase #4	$124.43	11.336%	$138.5354	$138.54	$138.55	$138.50
Purchase #5	$95.47	11.295%	$106.2533	$106.25	$106.25	$106.30
Purchase #6	$48.72	5.565%	$51.4313	$51.43	$51.45	$51.40
Purchase #7	$82.69	7.637%	$89.005	$89.01	$89.00	$89.00
7 purchase totals =	$647.97		$712.5614	$712.57	$712.60	$712.50