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	$150.55	11.820%	$168.345	$168.35	$168.35	$168.30
Purchase #2	$56.97	4.309%	$59.4248	$59.42	$59.40	$59.40
Purchase #3	$102.54	3.353%	$105.9782	$105.98	$106.00	$106.00
Purchase #4	$107.25	3.836%	$111.3641	$111.36	$111.35	$111.40
Purchase #5	$128.75	8.506%	$139.7015	$139.70	$139.70	$139.70
Purchase #6	$52.47	6.228%	$55.7378	$55.74	$55.75	$55.70
Purchase #7	$86.37	12.692%	$97.3321	$97.33	$97.35	$97.30
7 purchase totals =	$684.90		$737.8835	$737.88	$737.90	$737.80