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	$83.78	6.529%	$89.25	$89.25	$89.25	$89.30
Purchase #2	$48.62	5.206%	$51.1512	$51.15	$51.15	$51.20
Purchase #3	$170.80	8.758%	$185.7587	$185.76	$185.75	$185.80
Purchase #4	$84.83	5.566%	$89.5516	$89.55	$89.55	$89.60
Purchase #5	$211.48	10.335%	$233.3365	$233.34	$233.35	$233.30
Purchase #6	$25.94	3.213%	$26.7735	$26.77	$26.75	$26.80
Purchase #7	$27.53	8.575%	$29.8907	$29.89	$29.90	$29.90
7 purchase totals =	$652.98		$705.7122	$705.71	$705.70	$705.90