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	$79.94	12.637%	$90.042	$90.04	$90.05	$90.00
Purchase #2	$161.98	4.207%	$168.7945	$168.79	$168.80	$168.80
Purchase #3	$59.79	10.129%	$65.8461	$65.85	$65.85	$65.80
Purchase #4	$104.38	5.523%	$110.1449	$110.14	$110.15	$110.10
Purchase #5	$155.26	13.231%	$175.8025	$175.80	$175.80	$175.80
Purchase #6	$237.88	11.838%	$266.0402	$266.04	$266.05	$266.00
Purchase #7	$220.32	12.158%	$247.1065	$247.11	$247.10	$247.10
7 purchase totals =	$1,019.55		$1,123.7767	$1,123.77	$1,123.80	$1,123.60