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	$82.56	13.247%	$93.4967	$93.50	$93.50	$93.50
Purchase #2	$192.98	8.839%	$210.0375	$210.04	$210.05	$210.00
Purchase #3	$151.32	13.263%	$171.3896	$171.39	$171.40	$171.40
Purchase #4	$162.53	7.469%	$174.6694	$174.67	$174.65	$174.70
Purchase #5	$29.68	6.462%	$31.5979	$31.60	$31.60	$31.60
Purchase #6	$134.45	6.454%	$143.1274	$143.13	$143.15	$143.10
Purchase #7	$89.97	10.419%	$99.344	$99.34	$99.35	$99.30
7 purchase totals =	$843.49		$923.6625	$923.67	$923.70	$923.60