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	$173.56	10.120%	$191.1243	$191.12	$191.10	$191.10
Purchase #2	$175.95	11.697%	$196.5309	$196.53	$196.55	$196.50
Purchase #3	$6.80	3.341%	$7.0272	$7.03	$7.05	$7.00
Purchase #4	$44.92	6.816%	$47.9817	$47.98	$48.00	$48.00
Purchase #5	$61.39	11.211%	$68.2724	$68.27	$68.25	$68.30
Purchase #6	$85.47	13.603%	$97.0965	$97.10	$97.10	$97.10
Purchase #7	$28.97	12.199%	$32.5041	$32.50	$32.50	$32.50
7 purchase totals =	$577.06		$640.5371	$640.53	$640.55	$640.50