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	$139.63	13.236%	$158.1114	$158.11	$158.10	$158.10
Purchase #2	$69.73	3.596%	$72.2375	$72.24	$72.25	$72.20
Purchase #3	$198.98	11.676%	$222.2129	$222.21	$222.20	$222.20
Purchase #4	$29.79	6.260%	$31.6549	$31.65	$31.65	$31.70
Purchase #5	$233.61	3.768%	$242.4124	$242.41	$242.40	$242.40
Purchase #6	$10.32	10.521%	$11.4058	$11.41	$11.40	$11.40
Purchase #7	$139.37	3.113%	$143.7086	$143.71	$143.70	$143.70
7 purchase totals =	$821.43		$881.7435	$881.74	$881.70	$881.70