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	$39.30	6.515%	$41.8604	$41.86	$41.85	$41.90
Purchase #2	$91.63	8.737%	$99.6357	$99.64	$99.65	$99.60
Purchase #3	$46.55	10.378%	$51.381	$51.38	$51.40	$51.40
Purchase #4	$100.36	12.777%	$113.183	$113.18	$113.20	$113.20
Purchase #5	$234.38	8.172%	$253.5335	$253.53	$253.55	$253.50
Purchase #6	$30.45	10.641%	$33.6902	$33.69	$33.70	$33.70
Purchase #7	$73.46	6.577%	$78.2915	$78.29	$78.30	$78.30
7 purchase totals =	$616.13		$671.5753	$671.57	$671.65	$671.60