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	$170.52	6.472%	$181.5561	$181.56	$181.55	$181.60
Purchase #2	$110.67	8.865%	$120.4809	$120.48	$120.50	$120.50
Purchase #3	$228.71	3.617%	$236.9824	$236.98	$237.00	$237.00
Purchase #4	$18.51	8.616%	$20.1048	$20.10	$20.10	$20.10
Purchase #5	$98.39	7.255%	$105.5282	$105.53	$105.55	$105.50
Purchase #6	$48.57	11.450%	$54.1313	$54.13	$54.15	$54.10
Purchase #7	$72.61	13.134%	$82.1466	$82.15	$82.15	$82.10
7 purchase totals =	$747.98		$800.9303	$800.93	$801.00	$800.90