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	$79.58	13.609%	$90.41	$90.41	$90.40	$90.40
Purchase #2	$50.89	13.463%	$57.7413	$57.74	$57.75	$57.70
Purchase #3	$232.75	12.625%	$262.1347	$262.13	$262.15	$262.10
Purchase #4	$175.27	3.627%	$181.627	$181.63	$181.65	$181.60
Purchase #5	$7.80	11.371%	$8.6869	$8.69	$8.70	$8.70
Purchase #6	$35.38	4.238%	$36.8794	$36.88	$36.90	$36.90
Purchase #7	$110.73	11.351%	$123.299	$123.30	$123.30	$123.30
7 purchase totals =	$692.40		$760.7783	$760.78	$760.85	$760.70