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	$82.94	8.392%	$89.9003	$89.90	$89.90	$89.90
Purchase #2	$73.36	10.592%	$81.1303	$81.13	$81.15	$81.10
Purchase #3	$53.27	11.336%	$59.3087	$59.31	$59.30	$59.30
Purchase #4	$104.80	8.677%	$113.8935	$113.89	$113.90	$113.90
Purchase #5	$129.38	7.438%	$139.0033	$139.00	$139.00	$139.00
Purchase #6	$238.85	4.728%	$250.1428	$250.14	$250.15	$250.10
Purchase #7	$163.33	11.143%	$181.5299	$181.53	$181.55	$181.50
7 purchase totals =	$845.93		$914.9088	$914.90	$914.95	$914.80