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	$113.35	8.800%	$123.3248	$123.32	$123.30	$123.30
Purchase #2	$141.85	10.637%	$156.9386	$156.94	$156.95	$156.90
Purchase #3	$96.52	6.428%	$102.7243	$102.72	$102.70	$102.70
Purchase #4	$190.73	4.609%	$199.5207	$199.52	$199.50	$199.50
Purchase #5	$81.69	8.794%	$88.8738	$88.87	$88.85	$88.90
Purchase #6	$242.85	5.432%	$256.0416	$256.04	$256.05	$256.00
Purchase #7	$182.29	7.370%	$195.7248	$195.72	$195.70	$195.70
7 purchase totals =	$1,049.28		$1,123.1486	$1,123.13	$1,123.05	$1,123.00