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	$132.78	4.132%	$138.2665	$138.27	$138.25	$138.30
Purchase #2	$88.60	11.411%	$98.7101	$98.71	$98.70	$98.70
Purchase #3	$59.48	11.705%	$66.4421	$66.44	$66.45	$66.40
Purchase #4	$129.50	9.696%	$142.0563	$142.06	$142.05	$142.10
Purchase #5	$79.40	12.841%	$89.5958	$89.60	$89.60	$89.60
Purchase #6	$24.53	3.452%	$25.3768	$25.38	$25.40	$25.40
Purchase #7	$207.94	11.699%	$232.2669	$232.27	$232.25	$232.30
7 purchase totals =	$722.23		$792.7145	$792.73	$792.70	$792.80