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	$45.36	10.464%	$50.1065	$50.11	$50.10	$50.10
Purchase #2	$127.98	6.679%	$136.5278	$136.53	$136.55	$136.50
Purchase #3	$86.33	10.496%	$95.3912	$95.39	$95.40	$95.40
Purchase #4	$120.55	3.431%	$124.6861	$124.69	$124.70	$124.70
Purchase #5	$49.60	7.653%	$53.3959	$53.40	$53.40	$53.40
Purchase #6	$184.51	6.497%	$196.4976	$196.50	$196.50	$196.50
Purchase #7	$94.42	4.813%	$98.9644	$98.96	$98.95	$99.00
7 purchase totals =	$708.75		$755.5695	$755.58	$755.60	$755.60