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	$155.35	9.413%	$169.9731	$169.97	$169.95	$170.00
Purchase #2	$89.97	6.601%	$95.9089	$95.91	$95.90	$95.90
Purchase #3	$124.82	13.513%	$141.6869	$141.69	$141.70	$141.70
Purchase #4	$127.90	4.256%	$133.3434	$133.34	$133.35	$133.30
Purchase #5	$181.64	11.668%	$202.8338	$202.83	$202.85	$202.80
Purchase #6	$78.79	8.215%	$85.2626	$85.26	$85.25	$85.30
Purchase #7	$90.42	12.816%	$102.0082	$102.01	$102.00	$102.00
7 purchase totals =	$848.89		$931.0169	$931.01	$931.00	$931.00