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	$51.62	8.803%	$56.1641	$56.16	$56.15	$56.20
Purchase #2	$72.96	13.360%	$82.7075	$82.71	$82.70	$82.70
Purchase #3	$98.64	7.729%	$106.2639	$106.26	$106.25	$106.30
Purchase #4	$241.78	13.127%	$273.5185	$273.52	$273.50	$273.50
Purchase #5	$136.93	7.861%	$147.6941	$147.69	$147.70	$147.70
Purchase #6	$32.96	12.362%	$37.0345	$37.03	$37.05	$37.00
Purchase #7	$215.98	10.819%	$239.3469	$239.35	$239.35	$239.30
7 purchase totals =	$850.87		$942.7295	$942.72	$942.70	$942.70